United Kingdom and weapons of mass destruction

The United Kingdom is one of the five official nuclear-weapon states under the Treaty on the Non-Proliferation of Nuclear Weapons. It formerly possessed biological, and chemical weapons.

As of 2025, the UK possesses a stockpile of approximately 225 warheads, with 120 deployed on its only delivery system, the Trident programme's submarine-launched ballistic missiles. Additionally, United States nuclear weapons are stored at RAF Lakenheath since 2025, as well as between 1954 and 2008.

The UK initiated the world's first nuclear weapons programme, Tube Alloys, in 1941 during the Second World War. Under the 1943 Quebec Agreement, it was merged with the US Manhattan Project, but collaboration ended in 1946. The UK initiated an independent programme, High Explosive Research, testing its first nuclear weapon in 1952. After the British hydrogen bomb programme's successful Operation Grapple tests, the US resumed nuclear cooperation with the 1958 Mutual Defence Agreement. This has involved the exchange of classified scientific data, warhead designs, and fissile materials. UK warheads are designed and manufactured by the Atomic Weapons Establishment.

In total the UK conducted 45 nuclear tests, 12 in Australia, 9 in the Pacific, and 24 at the Nevada Test Site, with its last in 1991. The UK and France are the only two nuclear-armed countries that have ratified the Comprehensive Nuclear-Test-Ban Treaty.

During the Cold War, the UK developed a wide range of nuclear weapons delivery systems, primarily its strategic V bomber fleet, and the tactical WE.177 bomb. With a US agreement, it operated the Polaris fleet of ballistic missile submarines from 1968, replaced by the Trident fleet beginning 1994. The US supplied warheads under Project E, as well as the PGM-17 Thor missile, and hosted US systems including the Ground-Launched Cruise Missile, submarines at Holy Loch, and Strategic Air Command bombers.

The UK used chemical weapons extensively during the First World War, primarily chlorine, phosgene, and mustard gas, and in its intervention in the Russian Civil War employed adamsite. It possessed and researched chemical and biological weapons during and after the Second World War, centered at Porton Down. The causative agents of anthrax, plague, and tularaemia, and others were tested. After the war, the UK experimented with nerve agents such as sarin. In 1956, the UK renounced chemical and biological weapons, and later acceded to the Biological Weapons Convention and Chemical Weapons Convention. It completed destruction of its chemical stockpile in 2007.