The expansion of Britain’s nuclear arsenal provided for in soon-to-be resigned Prime Minister Keir Starmer’s Defense Investment Plan will contribute substantially to the global growth in nuclear spending that has already been underway over the last few years. The Ministry of Defense’s Nuclear Enterprise already consumed 18% of the defense budget, £10.9 billion ($14.6 billion), in 2024-25, and the Public Accounts Committee had projected that share would keep climbing to a full fifth of all military spending, Defense News reported on July 2. The International Campaign to Abolish Nuclear Weapons has separately calculated that Britain became the world’s third-largest nuclear spender in 2025, at $12.6 billion, putting it ahead of Russia. Only the U.S. and China are ahead of Britain.
Central to the current package is Astraea, the warhead designated A21/Mk7 that the Atomic Weapons Establishment has been developing since 2020 to replace the aging Holbrook design carried on Trident II D5 missiles, Defense News notes. Astraea is being developed “in parallel” with the US next generation W93 warhead and will share its Mk7 re-entry body, according to the government. The new British warhead’s estimated yield will reportedly fall somewhere between 90 and 455 kilotons, according to an analysis of publicly available information by the Nuclear Information Service, a U.K.-based nonprofit research organization.
