How Britain’s nuclear weapons are reliant on the US

The British government likes to tell us that its nuclear weapons system is independent. The reality is, however, that it is entirely dependent on the United States – both technically and politically. And the dangerous actions of the current US President have highlighted more than ever why we need to break up this not so special relationship. The bottom line is – it’s time to scrap Britain’s nuclear weapons and end our dependency on the US.

The US and the UK signed the Mutual Defence Agreement (MDA) in 1958, a bilateral treaty on nuclear weapons cooperation under which both countries agreed to exchange classified information to develop their respective nuclear weapon systems. The relevant part of the MDA used to be reviewed by Parliament every ten years, but in 2024 the government decided to amend the treaty to remove this requirement, guaranteeing the UK’s reliance on the US for its nuclear weapons programme indefinitely and removing any notion of parliamentary responsibility for this massive part of Britain’s defence policy.

As a result of this treaty, the UK’s nuclear weapons system is highly reliant on the US. The system comprises three components: the submarines, the missiles and the warheads.
While new Dreadnought-class submarines for Britain’s nuclear weapons system are being built in the UK – at the Barrow-in-Furness shipyard in Cumbria – many aspects of the design are based on US nuclear submarines. Additionally, many of the system’s components are bought from the US.

Both countries are using a shared Common Missile Compartment design for their submarines, with the UK contributing £12 million towards this in 2025, to enable compatibility between the UK and US launch systems. American company Lockheed Martin developed the navigation subsystem for the Dreadnoughts, with the work taking place in the US. Another American company, General Dynamics, is responsible for the fire control systems on both US and UK submarines.

The UK does not own its own missiles for the nuclear weapons system, instead leasing Trident II D5 missiles from the US. British submarines have to return regularly to the US base in King’s Bay, Georgia, for the maintenance and replacement of these missiles. The missiles were tested under US supervision at Cape Canaveral, off the coast of Florida. It emerged in 2017 that the US government may have even asked the UK government to cover up a failed nuclear missile test, denying British elected representatives the chance to scrutinise the viability of the nuclear weapons system.

Work has begun to manufacture new nuclear warheads for the UK. The current British warhead, the Mk4 Holbrook, is based on the US W76 design. The government has confirmed that the Mk4 uses US components for arming, the fusing and firing system, neutron initiators, the gas transfer system, and the aeroshell.

As well as being technically dependent on the US, Britain’s nuclear weapons are also far from being politically independent. They have been assigned to the US-dominated NATO since the 1960s, meaning they could be used against a country attacking another NATO member state. Since NATO has not adopted a no-first-use policy, it could also be used pre-emptively against another country that was perceived to be a threat.

Furthermore, it is inconceivable that the UK would ever use their nuclear weapons without the prior approval of the US.

Britain’s nuclear weapons therefore compromises, rather than asserts, British independence. We are militarily subordinated to Trump and his administration, meaning the Prime Minister fails to stand up to the US when needed.

It’s time for a truly independent defence and foreign policy, starting with getting rid of Britain’s nuclear weapons system as a first step towards their global abolition.