Britain deepens nuclear ties with France and Australia

Britain is deepening its nuclear relationships with the United States, France and Australia, with the Northwood Declaration recognising that there is no extreme threat to Europe which would not prompt a response by both Britain and France, according to the annual update to Parliament published this week.

The declaration, agreed in July 2025, reaffirmed and strengthened what the update describes as longstanding nuclear cooperation between the two countries. On the AUKUS partnership, the update records an important development in February this year when HMS Anson docked at HMAS Stirling near Perth.

The United States is described as Britain’s closest defence ally, with the relationship underpinned by long-standing cooperation on all nuclear matters including policy, operations and technology.

The practical expression of that relationship runs through the missile system, since Trident and its supporting systems fitted to the Vanguard class are manufactured in the United States, with Britain having bought title to a number of missiles drawn from a shared pool of assets under the 1963 Polaris Sales Agreement as amended for Trident in 1982. The system is operated independently by both the Royal Navy and the United States Navy.

The warhead fitted to those missiles is sovereign to Britain, with the Mk4A design maintained by AWE at Aldermaston, which also leads development of the replacement warhead, Astraea. Wes Streeting writes that the increase in investment across the enterprise “sends a clear signal of our commitment to global security, and to our Allies”, with the deterrent remaining declared to the defence of NATO.

The update states that nuclear deterrence is the cornerstone of NATO security and that the independent strategic nuclear forces of the United Kingdom contribute significantly to the overall security of the alliance, a declaration maintained since 1962.