The enhanced collaborations form part of the technical exchanges between the United Kingdom and the United States of America conducted under the auspices of the 1958 Mutual Defence Agreement, which support the UK's nuclear stockpile stewardship programme and contribute to the ongoing review of warhead options announced in the 2006 White Paper—The Future of the United Kingdom's Nuclear Deterrent (Cmd 6994). As was made clear in the White Paper, decisions on whether and how we may need to refurbish or replace our current warheads are likely to be made in the next Parliament and to inform these decisions we are undertaking a detailed review of the optimum life of the existing warhead stockpile and analysing the options that may be available.
In the interests of national security I am not prepared to discuss the detailed nature of these enhanced collaborations which commenced following an exchange of letters between Prime Minister Blair and President George W. Bush in December 2006.