With your permission, Mr. Speaker, I shall make a statement about the Government’s decision to maintain the United Kingdom’s independent nuclear deterrent.

There are many complex technical, financial and military issues to be debated in respect of this decision, but none of them obscures or alters the fundamental political judgment at the crux of it. Britain has had an independent nuclear deterrent for the past half century. In that time, the world has changed dramatically, not least in the collapse of the Soviet Union—the original context in which the deterrent was acquired. Given that that change has occurred, the question is whether it is wise to maintain the deterrent in the very different times of today. The whole point about the deterrent is not to create the circumstances in which it can be used but, on the contrary, to try to create circumstances in which it is never used. Necessarily, therefore, any analysis of what role it could play in any situation that is hypothetical will always be open to the most strenuous dispute.

Ultimately, this decision is a judgment—a judgment about possible risks to our country and its security, and the place of the deterrent in thwarting those risks. The Government’s judgment on balance is that, although the cold war is over, we cannot be certain in the decades ahead that a major nuclear threat to our strategic interests will not emerge; that there is also a new and potentially hazardous threat from states such as North Korea, which claims to have developed nuclear weapons already, or Iran, which is in breach of its non-proliferation duties; that there is a possible connection between some of those states and international terrorism; that it is noteworthy that no present nuclear power is, or is even considering, divesting itself of its nuclear capability unilaterally; and that in those circumstances it would be unwise and dangerous for Britain, alone of the nuclear powers, to give up its independent nuclear deterrent.

The House will notice that I do not say that the opposite decision is unthinkable, or that anyone who proposes it is pacifist or indifferent to our country’s defence. There are perfectly respectable arguments against the judgment that we have made. I both understand them and appreciate their force. It is just that, in the final analysis, the risk of giving up something that has been one of the mainstays of our security since the war, and, moreover, doing so when the one certain thing about our world today is its uncertainty, is not a risk I feel we can responsibly take. Our independent nuclear deterrent is the ultimate insurance. It may be—indeed, hopefully, is—the case that the eventuality against which we are insuring ourselves will never come to pass, but in this era of unpredictable but rapid change, when every decade has a magnitude of difference with the last, and when the consequences of a misjudgment on this issue are potentially catastrophic, would we want to drop this insurance, not as part of a global move to do so, but on our own? I think not.

What will happen from today, however, will be a very full process of debate. It is our intention, at the conclusion of that process in March next year, to have a vote in the House. We will make arrangements during the process to answer as fully as possible any of the questions that arise. Of course, I am sure the Select Committee on Defence, at least, will want to examine the issue carefully. The White Paper, which we publish today, goes into not merely the reasons for the decision but a technical explanation of the various options, and it tries to cover in some detail all potential lines of dispute or inquiry. I hope, therefore, that we can focus on the decision itself, not the process. Let me now turn to some of the key questions.

First, the reason why this decision comes to us now is that if in 2007 we do not take the initial steps toward maintaining our deterrent, shortage of time may prevent us from being able to do so. Necessarily, we can form that view based only on estimates, but they are from the evidence given to us by our own experts, by the industry that would build the new submarines, and from the experience of other nuclear states.

Our deterrent is based on four submarines. At any one time, one will be in dock undergoing extensive repair and maintenance, usually for around four years. The other three will be at sea or in port for short periods. At all times at least one will be on deterrent patrol, fully armed. The submarines are equipped with Trident D5 missiles that are US manufactured but maintained with our close technical and scientific collaboration. The operation of the system is fully independent—a missile can be fired only on the instructions of the British Prime Minister.

The current Vanguard submarines have a service life of 25 years. The first boat should leave service in 2017. We can extend that for five years, so in 2022 that extension will be concluded, and in 2024 the second boat will also end its extended service life. By that time, we will have only two Vanguard submarines. That will be insufficient to guarantee continuous patrolling.

The best evidence we have is that it will take us 17 years to design, build and deploy a new submarine. Working back from 2024, therefore, that means that we have to take the decision in 2007. Of course, all these timelines are estimates, but they conform to the experience of other countries with submarine deterrents, as well as to our own.

Secondly, we have looked carefully at the scope of different options. The White Paper sets them out—for example, aircraft with cruise missiles, but cruise missiles travel at subsonic speeds, and building the special aircraft would be hugely expensive; or a surface ship equipped with Trident, but that is a far easier target; or a land-based system with Trident, but in a small country such as the United Kingdom that would be immensely problematic and, again, an easier target. There is no real doubt on this score: if we want an independent nuclear deterrent, for a nation such as the UK a submarine-based one is the best. It is also our only deterrent; in the 1990s we moved to Trident as our sole nuclear capability.

Of the other major nuclear powers, the US has submarine, air and land-based capability. Russia has all three capabilities and has the largest number of nuclear weapons. France has both submarine and air-launched capability and has a new class of submarines in development, the last of which is due to come into service in 2010. China has a smaller number of land-based strategic nuclear weapons but is working on modernising its capability, including a submarine-based nuclear ballistic missile.

We will continue to procure some elements of the system, particularly those relating to the missile, from the United States, but, as now, we will maintain full operational independence. The submarines, missiles, warheads and command chain are entirely under British control, and will remain so after 2024. That gives British Prime Ministers the necessary assurance that no aggressor can escalate a crisis beyond UK control.

A new generation of submarines will make maximum use of existing infrastructure and technology. The overall design and manufacture costs of some £15 billion to £20 billion are spread over three decades, are on average 3 per cent. of the defence budget, and are at their highest in the early 2020s. As before, we will ensure that the investment required will not be at the expense of the conventional capabilities that our armed forces need. It is our intention that the procurement and building will, as now, be done by British industry, with thousands of British, highly skilled jobs involved.

However, we will investigate whether, with a new design, we can maintain continuous patrol with a fleet of only three submarines. A decision on that will be made once we know more about the submarines’ detailed design. No decisions are needed now on the warhead. We can extend the life of the D5 Trident missile to 2042. After that, there will be the opportunity for us to participate in any new missile design in collaboration with the US, which will be confirmed in an exchange of letters between myself and the President of the United States.

Maintaining our nuclear deterrent capability is also fully consistent with all our international obligations. We have the smallest stockpile of nuclear warheads among the recognised nuclear weapons states, and we are the only one to have reduced to a single deterrent system. Furthermore, we have decided, on expert advice, that we can reduce our stockpile of operationally available warheads to no more than 160, which represents a further 20 per cent. reduction. Compared with previous plans, we will have reduced the number of such weapons by nearly half.

So, inexorably, we return to the central judgment: maintain our independent nuclear deterrent, or not? It is written as a fact by many that there is no possibility of nuclear confrontation with any major nuclear power—except that it is not a fact. Like everything else germane to this judgment, it is a prediction. It is probably right—but certain? No, we cannot say that.

The new dimension is undoubtedly the desire by states, highly dubious in their intentions, like North Korea and Iran, to pursue nuclear weapons capability. Fortunately, Libya has given up its weapons of mass destruction ambitions and has played a positive role internationally; the notorious network of A. Q. Khan, the former Pakistani nuclear physicist, has been shut down. But proliferation remains a real problem. The notion of unstable, usually deeply repressive and anti-democratic states, in some cases profoundly inimical to our way of life, having a nuclear capability, is a distinct and novel reason for Britain not to give up its capacity to deter.

It is not utterly fanciful, either, to imagine states sponsoring nuclear terrorism from their soil. We know that this global terrorism seeks chemical, biological and nuclear devices. It is not impossible to contemplate a rogue Government helping such an acquisition. It is true that our deterrent would not deter or prevent terrorists, but it is bound to have an impact on Governments who might sponsor them.

Then there is the argument, attractive to all of us who believe in the power of countries to lead by example, as we seek to do in climate change and have done in respect of debt relief, that Britain giving up its deterrent would encourage others in the same direction. Unfortunately, there is no evidence that any major nuclear power would follow such an example—on the contrary. As for the new, would-be nuclear powers, it really would be naive to think that they would be influenced by a purely British decision—more likely, they would construe it as weakness.

Finally, there is one other argument: that we shelter under the nuclear deterrent of America. Our co-operation with America is rightly very close, but close as it is, the independent nature of the British deterrent is again an additional insurance against circumstances where we are threatened but America is not. Those circumstances are, I agree, also highly unlikely, but I am unwilling to say that they are non-existent.

In the end, therefore, we come back to the same judgment. Anyone can say that the prospect of Britain facing a threat in which our nuclear deterrent is relevant is highly improbable; no one, however, can say that it is impossible. In the early 21st century, the world may have changed beyond recognition since the decision taken by the Attlee Government more than half a century ago. But it is precisely because we could not have recognised then the world we live in now that it would not be wise, now, to predict the unpredictable in the times to come. That is the judgment that we have come to. We have done so according to what we think is in the long-term strategic interests of our nation and its security. I commend that judgment to the House.

Let me say straight away that I agree with the Prime Minister both about the substance of this decision and about the timing. It is a vital matter for our national security, and it requires a long-term approach. I hope that we can work together on this issue for the good of our country. Conservative Members have always believed that Britain should have an independent nuclear deterrent, and it is good to see that this is now so firmly part of a national political consensus.

When it comes to our nuclear deterrent, there are some straightforward questions to answer. Should it be replaced? Do we need a submarine-based system? Does the decision need to be taken now? Our approach to all those questions is to answer yes.

We believe that the case for maintaining our deterrent and therefore ordering a replacement is powerful. Those who argue that the world has changed so that no deterrent is required miss the point. Yes, the world has changed, and it continues to change rapidly, but that is the very case for keeping up our guard. Just as today’s threat is so different from that predicted 20 years ago, today we cannot predict the threat that we will face in 20 years’ time. Still less can we predict the threat in 40 to 50 years’ time, when the next generation of submarines will still be in service.

Some argue that because the major threat is now rogue states, a submarine-based alternative is not necessary. However, is not it the case that the replacement for Trident will cover the period 2025 to 2055, when the nature of threat is so unpredictable? It may be rogue states or major powers. We should have a credible deterrent to both. Does the Prime Minister agree that the key issue in deterrence is credibility, and that the key to a credible system is that it is not vulnerable to pre-emptive attack? Do not all the experts agree that, of the three options of land, air or submarine-based systems, the submarine-based system is the least vulnerable by far?

On the issue of timing, is not the key starting the design and procurement process so that the new submarines are available when the old ones go out of service? Would not a further life-extension programme be costly and uncertain and potentially leave a gap?

Let me ask about four specific matters. Will the Prime Minister confirm that it would not be right to rule out a fourth submarine? For example, the French deterrent requires four submarines. The Prime Minister said that the decision would be made when we know more about the detailed design. Will he confirm that the decision about the fourth submarine does not have to be taken until possibly as late as 2020?

Secondly, some have raised questions of disarmament and legality. Does the Prime Minister agree that replacing Trident with a submarine-based system does not hinder our efforts to achieve multilateral nuclear disarmament? Britain is not part of a nuclear arms race. Trident is our only nuclear weapon; it is a minimum deterrent and we have the right to replace it. On legality, will the Prime Minister confirm that maintaining such a deterrent is compatible with the provisions of the non-proliferation treaty?

Thirdly, there is the issue of cost. The White Paper gives a commitment that the cost will not come at the expense of the conventional capabilities of our armed forces. What does that mean for the defence budget that the Prime Minister is currently planning?

Fourthly and lastly, there is the issue of warheads. Previous Conservative Governments significantly reduced the number of warheads. The incoming Labour Government reduced them still further. Now the Prime Minister proposes yet another reduction. Is he content that the new total is sufficient to maintain a credible minimum deterrent? On that issue as others, does he acknowledge that he does not have to make concessions to those in the House who do not support the theory of deterrence and who have never supported Britain’s independent nuclear deterrent? Is not it the case that the Prime Minister can make the right decisions because he knows that, if he does, he will have our full support?

First, let me thank the right hon. Gentleman for his support for our decision. I essentially agree with the points that he made at the outset. In particular, I think that it is important to emphasise that the only credible deterrent is one that is not susceptible to pre-emptive attack—that is why the submarine-based system is so much better. On the design and procurement process, it is important that we get it under way now.

We certainly do not rule out four submarines. Indeed, it is the other way round—we would keep four unless it became feasible to move to three. If it is feasible to move to three, we can do that, but it depends on a series of discussions that will take place in the years to come about design and so on. The decision does not need to be made until much later.

It is clear in article VI of the non-proliferation treaty that we can maintain our independent nuclear deterrent. We are under an obligation, which we are fulfilling, to pursue multilateral negotiations, but there is no obligation on us to disarm unilaterally.

On the defence budget, all I can point to is the fact that over the past few years, after many years in which there were real-terms cuts in the defence budget, there have been real-terms increases. It is important that we give our armed forces the equipment and the defence spending that they require.

On the warheads, it is of course the case that it is only on the advice that retaining no more than 160 is consistent with maintaining a credible deterrent that we could take such a decision, and that is the advice that we have received.

As the Prime Minister and the White Paper both make clear, a decision to replace Trident is a significant decision, with enormous financial, political and security implications. To be properly made, that decision must take account of the strategic environment or threat assessment, of cost and of our treaty obligations. The Prime Minister says that the decision is a matter of judgment, and he is right; but it is my judgment that we can give proper consideration to all those factors only by postponing a decision, perhaps until 2014, by cutting the number of warheads by half to 100, and by extending the life of the existing submarines. There are many estimates available other than those contained—[Interruption.]

Order. The House should let the right hon. and learned Gentleman speak.

I remember the 1983 general election, when a large number of those people on the Labour Benches were arguing that there should be unilateral nuclear disarmament, that Britain should withdraw from NATO and that we should come out of the European Union. That just shows that if one waits long enough, one sees everything. The question in people’s minds is why is this decision being pushed through the Cabinet and Parliament just as the Prime Minister is about to leave Downing street. Is the decision about Britain’s interests or about his legacy?

I think that I gather from that that the right hon. and learned Gentleman is in favour of maintaining the deterrent, but not necessarily now. On this idea of postponing a decision, all we can do is go on the basis of the advice that is given to us. That advice is that, working back from 2024, when the second submarine goes out of service, it will take 17 years to put a replacement together. That is because there is a hugely complicated process of engineering and so on. That is the advice that we have received. I am not a technical expert, and nor is the right hon. and learned Gentleman. The political judgment is ours to make, but the technical advice that we have received is as I have outlined to the House. In those circumstances, I really do not understand on what basis I would stand here and say that we would put the decision back to 2014. The advice that I am receiving is that if we do that it is perfectly possible that we shall not be able to maintain the deterrent, so we shall have de facto taken the decision.

There are other estimates.

There may be other estimates, but I have to go on the ones that we have got—I cannot go on the Liberal Democrat one.

As for the reduction from 160 to 100 warheads, again, I do not know on what basis I would make that decision. We have already reduced the number significantly, but the evidence that we have is that we can reduce to 160 without damaging our deterrent. I cannot responsibly go beneath that number, when I have absolutely no basis on which to do that, other than the fact that 100 is a round figure. I cannot do that.

The right hon. and learned Gentleman is perfectly right in pointing to historical precedents, and I understand his point, but that is why it is a good idea not to go back there.

Those of us who have been here a long, long time find this a case of déjà vu all over again. Under a previous Government, I used the same arguments as my honourable and good friend the leader of the Liberal Democrats has used, when my assistant and I wrote the minority report for the Defence Committee. It was a brilliant report, but totally wrong. The arguments that I now hear against Trident were the ones that I used a quarter of a century ago.

One of the arguments was cost. Will the Prime Minister give us a ballpark figure, so that we have an indication of whether the cost of Trident will be as low as £15 billion, as some people hope, or as high as £76 billion, as projected by the Liberal Democrats?

The £15 billion to £20 billion cost is for the design, manufacture and infrastructure. In today’s money, that compares with the cost of the previous Vanguard submarines of some £14 billion. It is not as if we have nothing to compare with, and the experience of other nuclear states is also available for comparison. We are therefore reasonably confident of the estimate. Of course, there will be a massive amount of work to be done in the coming years, but my right hon. Friend is absolutely right that the evidence now is very clear that we need to start discussing the design next year. After all, a series of skills will need to be retained, and such highly qualified people will need to know that they will be retained, in order to do the work.

The Prime Minister promised us a debate, and I welcome the fact that it will run until March. Will he confirm, however, that the decision was not to replace Trident so much as to replace the Vanguard submarines that are its platform? Will he also confirm, as it was not entirely clear to me, that he was announcing in his statement that the United Kingdom was signing up to the United States’ service-life extension programme for the Trident D5 missile system?

Yes, we are doing that, as that will allow us to ensure that the missiles have an extended life. After that, we will be in a position to participate in the replacement of the Trident D5 missile. The right hon. Gentleman is also absolutely right that we are effectively talking about replacing the Vanguard submarines. If we want to maintain the submarine-based deterrent, however, we must begin consultation on that now.

I believe that the country will very much support the forthright position adopted by my right hon. Friend in tackling this difficult issue on behalf of the Government and Parliament. A successful conclusion to a healthy debate could do a huge amount to raise the esteem of Parliament. There is still, however, an educational job to be undertaken. All the arguments—there are legitimate ones on all sides—should be expressed, so that people can judge whether Parliament is making the right decision in some months’ time.

I totally agree with what my hon. Friend says. One of the reasons that I dealt with the matter at some length in my statement is that there are perfectly legitimate arguments that people should have. I genuinely think that the more that we debate the matter the more people will ultimately see that there are answers to some of the technical points, but, in the end, we are left with a judgment that, very responsibly, we should make as a House of Commons.

No one seriously doubts that, in the next 30 years, both rogue Governments and terrorist organisations will get access to nuclear, biological or chemical weapons, and will use those weapons to try to change the balance of power against the western world. Against that background, is not it the duty of responsible and democratic nuclear powers—not only the United States but Britain and France—to work together so that the countries of western Europe can make their full contribution towards our collective defence? Were we to give up that power unilaterally, would not that merely bring comfort to our enemies and alarm our friends?

I totally agree with the right hon. and learned Gentleman, and that is why we will continue to work with other countries in that vein. The NATO summit last week emphasised again that that collaboration is as important as it has ever been. The point about our duty to work together with other countries on nuclear disarmament is absolutely right. Were we to pursue that in any other way, that would go against what we all wish to see.

Given a cost of up to £75 billion—including the cost of maintenance over a lifespan of 30 years—how can this proposal be justified in an utterly different, post-cold-war environment, when it will severely restrict much more needed conventional defence expenditure? It will clearly undermine the nuclear non-proliferation treaty, especially for Iran, and it will drain off colossal sums of money from where they are most needed to deal with the real threats that confront us—terrorism, climate change and long-term energy insecurity.

Obviously, I do not agree with my right hon. Friend. We will be able to maintain the replacement for Trident with the same percentage of the defence budget for running costs with which we maintain the existing deterrent. The cost that we are giving is the cost of maintaining that submarine capability.

I do not agree with my right hon. Friend that the proposal is contrary to our obligations under the non-proliferation treaty. Article VI states

“Each of the Parties to the Treaty undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament”.

In other words, there are obligations to pursue negotiations in good faith with other countries. That is precisely why it is clear that we are fully able to maintain our existing nuclear deterrent under the non-proliferation treaty.

Of course, my right hon. Friend is absolutely right to say—as I said in my statement—that the cold war is no longer with us; but the one thing we cannot say is that there are not potentially new and hazardous security threats out there, and in any event there are still major nuclear powers. I agree that it is—let us say—highly improbable, highly unlikely, that we will ever be threatened by any of those powers, but I am certainly not prepared to say that such a thing is impossible to think of. I believe that we must be in a position to protect ourselves against every potential threat, and ultimately I think that giving up our independent nuclear deterrent in what is a very uncertain and insecure world would be irresponsible.

The Prime Minister pointed out that close co-operation with the United States of America would be very important, not just in terms of politics but in terms of the upgrading of technology. Can he assure us that in the event of the Americans’ improving their missile warhead system in the future, we will have the same kind of access that we have today?

The whole purpose of the agreement into which we are entering with the Americans is to give us access to that technological improvement. As the Americans develop the successor to the Trident D5 missile, we will be able to work with them closely and have access to that updated weapon system. Although the deterrent would be used in wholly independent circumstances relating to the United Kingdom, the ability to work with the Americans is very important.

The Prime Minister is right to remind the House that we are not experts on this subject, but Theodore Postol is. Let me explain for the House’s benefit that Theodore Postol is a professor of physics at Massachusetts Institute of Technology. He is also the former United States official responsible for the development and implementation of the Trident II system. He told me at the weekend that the American equivalent of the Vanguard class of submarine, the Ohio class, lasted 45 years despite having twice as much sea time as our boats, and that the Americans are currently converting some of their Trident-carrying boats into cruise-carrying submarines. Does the Prime Minister agree with Ted Postol? Could we not convert some of our boats, and avoid disproportionate expenditure?

First, let me tell my hon. Friend that I am delighted to see him back in his place. Secondly, let me tell him that the question whether we could do the same as the Americans has been gone into in a great deal of detail, and I am advised that the answer is no, because their submarines were designed and fitted in completely different way. I am told that the life of our boats cannot be extended for longer than five years.

Obviously some of the issues are highly technical, and, as I say, I am not an expert, but the best advice we have is that it is not possible to do what the Americans are doing because their submarines are different from ours, and that the maximum safe extension for ours is five years. That is why this decision arises now.

May I follow on from the question from the hon. Member for Liverpool, Walton (Mr. Kilfoyle)? Does the Prime Minister agree that just as vital as maintaining our independent nuclear deterrent is protecting the interests of the taxpayer and value for money, particularly since this replacement is going to cost £20 billion, and starting? Should not we have a debate on whether there are other options? After all, the multiple warhead was designed to protect Moscow defences from attack, which is unlikely to occur in the future. Why should we rule out at least consideration of cruise missiles being launched from our attack nuclear submarines? What would that cost? Would it not be a fraction of the cost of this system?

For that very reason the White Paper goes into the different systems in some detail. I agree that one of the issues is: should we stick with the submarine-based system, or should we move to some other type of system? All I can say is that, for the reasons given in the White Paper, the submarine-based system is, in my judgment, the most suitable form of deterrent. One can go through the other options, which are all well known. In the debate over the coming months, people can canvass all those different options, but the difficulty is that an aircraft armed with cruise missiles is far easier to intercept and the cruise missiles go at subsonic speeds. In any event, in terms of cost, I am advised that the aircraft would have to be specially designed and that is an enormously expensive undertaking. We could have a surface ship armed with Trident missiles, but that is an easier target. Alternatively, we could have land-based silos. It is worth pointing out that America, for example, has land-based silos as well as air-launched and submarine-launched missiles. Its land-based silos are situated in a vast territory—a huge area can be used for that purpose. I do not think that that is practical for us. Therefore, there are very good cost reasons why it is best to stick with the submarine-based missile. This is precisely the type of issue that the next few months will allow us to consider. The White Paper goes through those options in detail—this is why I wanted the White Paper—so that the perfectly legitimate questions that have been raised can be answered.

I welcome the Prime Minister’s statement, which will be particularly welcomed by those who work in DML and the naval base in Plymouth. Does he agree that on this occasion we are indeed talking about rocket science of the most complex and challenging kind and that the people who design, integrate and make the safety case for this equipment have to have many years of training and experience? For that reason alone, those who call for postponement are simply wrong.

My hon. Friend is entirely right. It is worth pointing out that thousands of people who work in and around her constituency have built up expertise over the years that we cannot afford to lose, and nor can their employers afford to keep those skills extant in circumstances where it is unclear for several years whether we will proceed. One of the reasons why this process will take slightly longer is that the submarine industry in our country and indeed in other parts of the world has contracted, so my hon. Friend’s comments are absolutely right. If we allow those skills to degrade—I think that that would be the most irresponsible thing of all—we will take a decision without ever meaning to take a decision.

The credibility of Trident in the previous century depended on the belief that we would be prepared to use it if necessary against an overwhelming enemy. Are we seriously to believe that we would ever use that most potent nuclear weapon against the rogue states or terrorist organisations that are the enemies of today and likely to be the enemies of tomorrow? Why will the Prime Minister not at least explore more flexible, more useable and therefore more credible non-nuclear alternatives before taking a final decision?

With respect, the whole principle of deterrence is that we do not state the precise circumstances in which we might use that deterrent, since that very uncertainty is part of the concept of deterrence, but we all have to make a judgment about that. Of course, it is possible to say, “Let us get rid of our independent nuclear capability and rely simply on conventional forces.” In the end, I do not think that that is sensible for the reasons that I gave in my statement: first, I do not think that we can say that it is inconceivable in any set of circumstances that we could be subject to a major power's nuclear threat; secondly, we have additional states that are developing nuclear weapons capability, and who can say where that capability will lead in years to come? I am, frankly, also somewhat fortified in this judgment by the fact that no other major nuclear power is taking the step of getting rid of its independent deterrent; indeed, it is interesting that France, for example, is in the process of launching a new generation of submarine-based nuclear missiles. Therefore, the whole idea of us at this point in time saying that we will put it out of our power to maintain our independent nuclear deterrent seems to me on balance to be wrong. I do not in the least dispute that it is possible to make the other point of view, but in the end there is a judgment to be made, and we shall all have to make it when the time comes to vote.

Can the Prime Minister confirm that, in contrast to what happened in 1947, 1961, 1974 and 1980, this Prime Minister and this Government have for the first time ever initiated a public debate on these decisions? Will he also confirm that the Government remain committed to the goal of global nuclear disarmament and will make renewed efforts to secure international negotiations as called for under article VI of the non-proliferation treaty?

Yes, I can confirm that, and it is important that we have a full debate because, as is clear, there are different views in all parts of the House in relation to this debate. The trouble is, however, that in the end it comes down to a judgment. The difficulty is that we cannot predict the precise circumstances in which the relevance of our nuclear deterrent will arise; we can only make a judgment about that. The truth is—I think we all struggle with this when coming to a decision—that although the world in which we live has changed dramatically since the 1940s, there is still a threat out there. Indeed, that threat can change, and even be extended in certain dimensions.

Therefore, is it sensible for us to say now—at this point—that we are going to give up an independent nuclear deterrent that has been one of the mainstays of our defence for over half a century? We can debate all the technical, financial and military questions, but we come back to that simple judgment. When I was reflecting on the decision, I reflected on this: what would it be like if I were to come to the Dispatch Box as Prime Minister and say, “We have decided that we are going to give up our independent nuclear deterrent”? I cannot see that; I just cannot see it.

Given that Scotland has a national Parliament not a parish council, will the Prime Minister give an assurance that he will respect the Scottish Parliament when it votes against the stationing of nuclear weapons in Scotland?

I always respect the Scottish Parliament because it is part of the devolution settlement within the United Kingdom, and unlike the hon. Gentleman, I believe that Scotland is stronger and better within the United Kingdom than it would be out of it.

As a Member of Parliament who does not believe in weapons of mass destruction even though they might be a deterrent because I do not think that we would ever dare use a deterrent that would destroy the world, I want to know whether the Prime Minister thinks that the money spent on them would be better spent on tackling poverty in Africa—and poverty in this country after last week’s report—and pensions for old people?

Again, that is a perfectly understandable judgment for people to come to. Some would say, “Spend this money on conventional defence.” My hon. Friend says, “Don’t spend it on defence at all, but spend it on poverty reduction programmes, or public services in our country.” But in the end the question is: will we make our country less safe if we give up this deterrent? [Interruption.] The purpose of deterrence is not so that we can use it; the whole purpose of deterrence is so that we never have to use it, and that is the reason that we keep it.

In welcoming this hard decision, I ask the Prime Minister to reassure us that he truly understands the philosophy of deterrence, which is complicated and tough. For instance, does he agree that our negotiating position is always strongest when we keep all our military options open, which is the opposite of what we did over Iran?

It is very important that we keep all our options open, which is precisely the reason why we are better able to achieve multilateral disarmament if we maintain our own deterrent.

If the British Government decided to go it alone and to act without our allies, would they first have to seek the approval of our American allies?

Our deterrent in its operation is completely and totally independent. As I said, I am not speculating on the circumstances in which we might or might not use our deterrent, but it is completely operationally independent. It is a decision for the British Prime Minister and the British Prime Minister alone.

The Prime Minister is right to say that this successor submarine must be built with British technology and by British scientists, but does he share the extreme anxiety of Rolls-Royce—one of the main contractors—that not enough nuclear physicists are coming out of British universities with the necessary specialism to enable it to be sure of doing the job that he outlines today? What steps will he take to reverse the decline in physics in schools and universities, so that we can be sure that we have enough British scientists with the necessary security clearance to build these submarines?

In the years to come, thanks in part to the fact that we have doubled the science budget, there will be many more opportunities for people in British science. The skills that we require is one of the issues that we will discuss with companies when we begin this process next year.

If a decision is to be taken by Parliament in three months’ time, will my right hon. Friend confirm that a recent document circulated to us all by Greenpeace, containing figures running into millions of pounds in expenditure on this programme, is complete fiction?

What people do is that they take all the existing running costs and project them forward for many years. The best estimates that we have of the actual costs of the design, manufacture, infrastructure and so on are the £15 billion to £20 billion estimates. We are somewhat strengthened in saying that, because the cost of the present Vanguard submarines—in today’s terms, not in the financial terms of the period in which they were built—is about £14 billion. We also have a lot of experience, not least in terms of the French system that is being brought into being.

The right hon. Gentleman relies on his judgment, but does he recognise that it was the very judgment that took us into Iraq, and that his reputation for good judgment is not highly regarded? That being so, if he wants to carry this thing forward, perhaps this House needs some independent advice. Might I commend early-day motion 239, which is in my name? It suggests the appointing of seven Privy Councillors to advise this House on the cost of Trident and the alternatives, and that this House should not vote on the matter until we have received such a report.

Obviously, I do not agree with the right hon. and learned Gentleman on Iraq. In the end, this is not a judgment that can be subcontracted to other people; the Government have to take a decision. We have said that we will put this decision, after a debate, to the House and the House will vote on it. Rather than endlessly sidetracking ourselves into questions of process, we should just come to a judgment.

May I thank my right hon. Friend for his statement? Given the importance that he attaches to an independent nuclear weapons system for the UK, would he advise the 23 non-nuclear NATO states to acquire similar independent nuclear weapons, and if not, why not?

No, I would not, and for the very reasons that are at the heart of the non-proliferation treaty. It is clear that those who are the major nuclear powers can remain nuclear powers, fully consistent with the non-proliferation treaty. To be fair, over the years that treaty has worked reasonably well, in that some countries have given up their nuclear weapons ambitions, such as Brazil, South Africa and so on. In fact, some of the predictions that were made back in the 1960s about the number of nuclear states that there would be have fortunately turned out not to be correct. But it is recognised, and it is at the heart of the non-proliferation treaty, that Britain, along with those other countries, should be able to be a nuclear power.

Given that NATO prohibits Germany from having nuclear weapons, and that we are apparently using NATO for missions further and further afield, has the Prime Minister discussed the nuclear deterrent in the context of article 5 of the NATO treaty, the prohibition affecting Germany, the proposal to change the European security and defence policy and the defence requirements, and European integration?

No is the answer to that.

Would my right hon. Friend agree that if his recommendation is accepted, it would be possible for a future Parliament in 2014 to decide not to implement a Trident replacement, but it would not be possible for that Parliament to implement a Trident replacement if this Parliament decides not to?

There are sufficient experts on parliamentary sovereignty in the Chamber that I think that I am on strong ground in saying that Parliament can always decide what it wishes to do. However, let us be clear that if we were to endorse the Government’s decision next March we would be proceeding with a series of designs and assessments with the industry concerned. It is correct that it is only at a later stage that we will let the contracts, and it is always open to any Parliament to do anything, but it is highly unlikely to alter the decision that, frankly, will effectively be made next March.

The hon. Member for Moray (Angus Robertson), who speaks for the Scot nationalists, made an important point that the Prime Minister rather dodged: that in the unlikely eventuality—heaven forfend—of an Scot nats majority in the Scottish Parliament, perhaps through a Liberal Democrat coalition, it is possible that we would face a non-nuclear Scotland. In which case, a submarine-based deterrent would not be possible. Has the Prime Minister thought about what alternative might be necessary under those circumstances?

First, I am not prepared to engage in that hypothesis, for obvious reasons. Secondly, my experience is that people in Scotland are every bit as committed to the defence of the United Kingdom as people elsewhere.

The House has listened to what my right hon. Friend has said about the weapons and the possibility of reducing from four to three submarines. But will he acknowledge my concern that the announcement that the UK will upgrade its nuclear weapons system will weaken our efforts to persuade other states to stay non-nuclear and could undermine the world’s non-nuclear proliferation mechanisms?

First, what we are actually doing is maintaining the independent nuclear deterrent. Indeed, we will reduce the number of warheads that we have. Secondly, that is not the evidence. The evidence is that the non-proliferation treaty works best in circumstances in which there is a multilateral mood for disarmament. That is the reason why we believe it is better to pursue such a course under the terms of that treaty. Suppose Britain said that we would no longer maintain our independent deterrent. Would France reverse its decision? No. Would any of the other major nuclear powers say that they would not maintain an independent deterrent? No. Would Iran or North Korea give up pursuing their nuclear weapons ambitions? No. The reality is that my right hon. Friend’s aims—which I fully support—will only be achieved by working together.

The Prime Minister will accept that for Trident’s replacement to be a credible deterrent it has to be truly independent. Will he therefore explain to what extent Britain will depend on the US for the operational capability and command chain of the new system?

The answer to that is very clear. Our present nuclear deterrent is fully operationally independent and will remain so. Only the Prime Minister can authorise its use. The instruction to fire would be transmitted to the submarine using entirely UK codes and equipment and all the command and control procedures are totally independent. It is particularly true that this operational independence is at the heart of our being able to say correctly that we have an independent nuclear deterrent. It can be used and fired only at the instigation of the British Prime Minister—in other words, of Britain. It is correct that we procure elements of our deterrent system, especially the missile, from the United States, but every single factor that leads to its command and control is in our own hands. The hon. Gentleman is right that it is important that we make that completely clear to people because it is the whole basis on which we have our independent deterrent.

Is the Prime Minister aware that the logic of his proposal will be to increase nuclear weapons around the world and that as Professor Joseph Rotblat, a Nobel peace prize winner and a nuclear scientist, made plain before he died, if powerful countries feel insecure and therefore need nuclear weapons, who on earth are they to proselytise or argue against weaker countries also obtaining nuclear weapons to protect themselves? Does not the Prime Minister think that the security of the 21st century would be better served by seriously pursuing disarmament rather than rearmament?

There are two problems with what my hon. Friend says. The first is that we are maintaining our existing independent capability; indeed, we will be maintaining it with fewer warheads than we have at the moment. Secondly, the non-proliferation treaty is the agreement of the international community on the issue. At the heart of the treaty is the recognition that there will be major nuclear power states, of which Britain is one. There is then an obligation in the course of the treaty to pursue disarmament through negotiations under article VI, as I pointed out. In actual fact, what we are doing is fully consistent both with the treaty and with not increasing, or indeed upgrading, our system, but maintaining the level of deterrence we have at the moment, albeit, possibly, with fewer submarines and certainly with fewer warheads.

May I commend the Prime Minister’s statement, particularly the part that referred to the need for a debate? Does not such a debate need to go much wider than the question of our nuclear deterrent? Is not the Government’s foreign and defence policy somewhat in disarray following events of the last two or three years, and do not we need to put the decision in the proper context of a reassessed foreign and defence policy, to give the people of this country confidence in what the House is about to decide?

The hon. Gentleman is entitled to make any points he wants in the course of the debate. He can debate the matter in any context he wants and make suggestions as to why the foreign and defence policy of this country is wrong, but I can tell him that the policy we have pursued is based on a strong alliance with the United States of America and a strong partnership within the European Union. That is where I stand, and that is where the Government stand; if he wants to stand somewhere different, that is up to him.

May I press my right hon. Friend on one aspect of the central judgment that he talks about? He says that it is not fanciful to think that in the future a rogue state might sponsor nuclear terrorists, but surely it is fanciful to suggest that we might use our nuclear weapons in retaliation against such a rogue state.

Again, my hon. Friend is absolutely right to say that these are fine matters of judgment in difficult circumstances that we are, of necessity, predicting—they are hypothetical. I can see a situation—let us hope it never happens—in which states with their own nuclear weapons capability are sponsoring terrorism and encouraging the use of chemical, biological or nuclear weapons capability. We do not ever want to be in the position of using our deterrents, but if states had nuclear weapons capability and were threatening our country, they might be less willing to do so if we had the nuclear deterrent. That is the judgment that we have to make. I repeat that the idea of the deterrent is not to use it but to try to create circumstances in which it is never used, which is why when people debate the morality of having nuclear weapons or not, it is merely another way of having the debate about whether deterrents deter. If they deter, it is sensible to have them; if they do not, obviously it is not. That is why this thing is best decided on the basis not of what we might do in a particular situation but of what might deter others in actions we wish to deter.

In paying tribute to the measured way in which the Prime Minister put forward his argument today, may I underline the point made by the hon. Member for Newcastle upon Tyne, North (Mr. Henderson) about the necessity to extend the debate not just to the Chamber but to the country as a whole? In doing so, will the Prime Minister pay tribute to the thousands of people who work at the Atomic Weapons Establishment at Aldermaston and make the point that it is not just a centre of excellence for engineering and science in the narrow area of atomic weapons, but that its benefits are felt in the wider economy as a whole?

I certainly pay strong tribute to people who work at the Atomic Weapons Establishment at Aldermaston. I know that about 4,000 people—some of the most highly skilled scientists and engineers—are employed there at the moment. Of course the debate will go wider than Parliament—so it should—and people will have an opportunity over the coming months to debate the issue in whatever context they wish to debate it. Some who work at those establishments will also have something to contribute—at least to be able to dispel some of the myths that surround issues to do with timing, the viability and capability of the submarines and so forth. I totally agree with my hon. Friend the Member for Newcastle upon Tyne, North (Mr. Henderson) that the broader the debate, the better for the country. In the end, it is a decision of such importance, and we take it in somewhat different times than they were, that people expect the debate to be more open—and it will be.

May we take the case of Iran? May I invite my right hon. Friend to consider that there is widespread concern in the House that a state such as Iran, given the prospect of the UN not being able to dissuade the country, is more likely to use an independent nuclear deterrent against democratic states within its own region? We know that Iran sponsors the Taliban and Hezbollah. Concern is based more on that than on the potential threat of Iran using the weapons against Britain. May I invite my right hon. Friend to say a word or two more about how, in those circumstances, Britain’s retaining an independent nuclear deterrent will assist the world to dissuade a country such as Iran from threatening or even using its weapons?

Again, it is possible to speculate and hypothesise, but my right hon. Friend is essentially correct in saying that those in the immediate neighbourhood of Iran may feel a greater sense of threat. The one thing that is obvious from today’s world is that countries like our own are working alongside others—in Afghanistan, for example—and those others can be impacted by the actions of a nation like Iran. Because of the greater interdependence of the world today and particularly in the context of the global terrorist threat, it is not possible to compartmentalise the problem and draw a line around the middle east or part of Asia as a region. That is simply not possible. Although at the present time, the more immediate threat may well be felt in the neighbourhood, we cannot say that it will not go broader than that in the years to come.