To ask the Secretary of State for Defence in which years since 1990 experiments have been carried out with the United States on US warhead designs and nuclear weapons technology. (265113)

Research, including trials, and experiments, is conducted on a regular basis, by the Atomic Weapons Establishment as part of its responsibility for maintaining the safety, security, and effectiveness of the UK nuclear stockpile in the absence of live testing. Some of this research, is undertaken in collaboration with the United States under the auspices of the 1958 Mutual Defence Agreement.

Following publication of the 2006 White Paper, “The Future of the United Kingdom's Nuclear Deterrent” (Cmd 6994) and the subsequent exchange of letters between Prime Minister Blair and President George W. Bush in December 2006, additional research is currently being undertaken, some in collaboration with the US, on how we may need to refurbish or replace our current warheads to help inform decisions, likely to be made in the next parliament.

I am withholding the detail of this collaboration in the interests of national security.