The United Kingdom is now in a nuclear weapons buildup program to deal with the “current security environment.” This resulted from a new nuclear weapons defense doctrine contained within the 2021 and 2025 U.K. Strategic Defense and Security Reviews (SDSRs), which are issued by the Prime Minister and overseen by the Secretary of Defense.
The U.K. Parliament document, “Nuclear Weapons Profile: United Kingdom,” of June 26, 2025, reported that the 2010 SDSR had called for a “65% reduction in the size of [the United Kingdom’s] overall nuclear stockpile since the height of the Cold War.” However, the Federation of American Scientists reported that the 2021 SDSR called for the reversal of the U.K. plan to reduce its nuclear stockpile from 225 warheads to 180 warheads, and instead proposed that the U.K. increase its stockpile of nuclear warheads to “no more than 260 warheads.” Currently, the U.K. obtains its warheads from the United States, but now it will produce and maintain its nuclear warheads at the Atomic Weapons Establishment (AWE) facilities in Berkshire, England, including specifically the Aldermaston AWE facilities for design and manufacturing. These facilities, for security reasons, will not release the number of new nuclear warheads that have been produced thus far.
There is an important hitch: The U.K. cannot expand its nuclear weapons arsenal without the support of the U.S., as Aldermaston AWE depends on design and engineering data that it receives from the U.S. under the 1958 Mutual Defense Agreement, an agreement that was extended in perpetuity by the Biden Administration.
At the same time, as a consequence of the 2025 SDSR, with respect to the submarines that will deliver these nuclear warheads from under the ocean, the U.K. will replace its existing fleet of four Vanguard-class submarines (SSBN) with a new Dreadnought-class of SSBN, of which four are planned. The plan is to produce one Dreadnought-class submarine every 18 months. Each submarine would carry 16 missiles. So far, £15 billion have been allocated toward this project.
