From: Ministry of Defence Annual Report and Accounts 2007-2008 Volume I: (page 39)
"28. The UK’s Trident submarine force has maintained a continuous and independent nuclear deterrent capability at sea, in support of NATO and as the ultimate guarantee of our national security." In June 2007 HMS Vengeance completed the 300th Continuous At Sea Deterrence patrol. Since April 1969 there has been a Royal Navy deterrent submarine continuously on patrol somewhere in the world.
Following the House of Commons endorsement in March 2007 of the Government’s proposals for maintaining the UK’s nuclear deterrent capability by procuring a new class of submarines to replace the Vanguard-class and joining a programme to extend the life of the Trident II D5, work began on the detailed concept phase for the new submarines and on taking forward participation in the Trident
II D5 life extension programme.
The MoD has continued the programme of investment in sustaining capabilities at the Atomic Weapons Establishment, both to ensure the UK can maintain the existing warhead for as long as necessary and to enable us to develop a replacement warhead if that is required. To inform a decision on whether and how we may need to refurbish or replace this warhead, which are likely to be necessary in the next Parliament, work was taken forward to review the optimum life of the existing warhead and to identify the range of replacement options that might be available."