Nuclear weapons of the United Kingdom

The United Kingdom maintains a stockpile of about 225 warheads and is the only nuclear-weapon state that currently relies on a single delivery system: four Vanguard-class submarines based at Faslane, which maintain the continuous at-sea patrol the Royal Navy has kept since 1969. About 40 warheads are carried on the boat at sea, with 48 missiles available for the three operational boats. Their Trident II D5 missiles are drawn from a pool shared with the US Navy, and the warhead design is closely related to American counterparts under the 1958 US-UK Mutual Defence Agreement, renewed indefinitely in 2024. Dreadnought-class replacement submarines, all four under construction, are due from the early 2030s; SIPRI reports that the Vanguard boats' service lives have been extended to about 37-38 years, with patrols reportedly lasting 150-200 days, and that the UK has not conducted a successful Trident test in over a decade, the 2024 attempt having failed.

In 2021 London raised its self-imposed stockpile ceiling to 260 warheads and stopped publishing detailed figures. On 24 June 2025 it announced the purchase of 12 nuclear-capable F-35A aircraft and its intention to join NATO's nuclear sharing arrangements as the alliance's sixth host nation, returning the Royal Air Force to a nuclear role for the first time since the WE.177 bomb was retired in 1998, with US B61-12 bombs remaining in American custody. The aircraft will be based at RAF Marham, with the nuclear mission from the early 2030s; the Ministry of Defence's Defence Nuclear Enterprise annual update of 15 September 2026 confirmed the role.

Britain tested first at Monte Bello in 1952, conducted its last test in 1991, and has ratified the CTBT. It is a nuclear-weapon state under the NPT and committed, like the other four, to eventual disarmament under Article VI.

The 2025 Strategic Defence Review reframed the deterrent around readiness: sustaining the continuous patrol with an aging Vanguard fleet, delivering Dreadnought, and funding, with 15 billion pounds, the sovereign Astraea replacement warhead first announced in 2020, which SIPRI expects in service in the late 2030s or early 2040s. In July 2026 the government set out 63 billion pounds of spending on the deterrent over four years; the nuclear enterprise cost 10.9 billion pounds in 2024-25, about 18 percent of the defence budget. US B61-12s are reported possibly back at RAF Lakenheath: a transport flight from Kirtland Air Force Base that landed there on 17 July 2025 was widely reported as the first US nuclear delivery to Britain since 2008, but FAS notes the base's upgrades were incomplete and SIPRI lists the UK only as "possibly" hosting the bombs. The 260 ceiling stands, and London no longer publishes deployed figures.

Britain is also drawing closer to France. The Northwood Declaration of 10 July 2025 stated that the two countries' nuclear forces "can be coordinated", a joint Nuclear Steering Group met for the first time in December 2025, and in March 2026 the UK was among the eight countries that expressed interest in France's "advanced deterrence" initiative.