UK has begun the programme for implementing the reductions in the number of UK nuclear warheads, as declared in the Strategic Defence and Security Review (SDSR) 2010.
As part of the review, the number of warheads on each submarine will be reduced from 48 to 40, the number of operational missiles on the Vanguard Class submarines will be reduced to eight, and the number of operational warheads from 160 to 120.
Defence Secretary Liam Fox said the reduction has been enforced on at least one of the Vanguard Class ballistic missile submarines (SSBN) and the changes across the fleet will be completed within the constraints of the deterrent's operational programme.
"On current plans, our expectation is that the subsequent reduction in our total stockpile to no more than 180 warheads will complete by the mid 2020s," Fox added.
According to the SDSR, the UK's deterrence requirements can be effectively met with a smaller nuclear weapons capability.