The Trump administration’s volatile approach to its allies has forced the UK to reconsider fundamental pillars of its defence policy, including whether it can rely on the US. This extends even to the UK’s nuclear deterrent, with many questioning whether the UK needs a nuclear weapons system that is less dependent on the US for maintenance and support.
Unlike most US allies in NATO, the UK is officially a nuclear weapons state, and therefore less reliant on Washington’s nuclear extended deterrence guarantee. It has its own nuclear weapons system, Trident, which is based in Britain and ostensibly operates independently.
However, Trident is closely linked to the US’s nuclear programme, raising concerns about its independence. The missiles are US-built, and the system relies on the US for maintenance.
Trident is also expensive, absorbing about 6 per cent of the UK’s defence budget in 2023 – though changes to the way UK Defence classifies spending on nuclear issues means it’s now difficult to say how much Trident on its own costs every year. Aside from the cost, alternative nuclear deterrent strategies – including partnership with France or a wider European scheme – pose their own challenges.
The UK government therefore faces a difficult choice, with no easy options.
Trident is comprised of the UK’s four Vanguard class nuclear-powered, nuclear-armed submarines. The UK deploys one of these submarines at all times, in line with its ‘Continuous At-Sea Deterrent’ policy, or CASD.
The submarines are based at Faslane, near Glasgow, and are currently being replaced by new Dreadnought submarines, being built at Barrow-in-Furness in Cumbria.
In day-to-day operations, the UK’s Trident programme is completely independent from the US. The British Prime Minister can launch the missiles without any external input.
However, while operationally independent, Trident is a US-built missile system and the UK’s nuclear capabilities currently rely on the US in several ways. The UK invested in Trident’s research and development, and purchased the missiles from the US under the terms of the modified Polaris sales agreement, updated in 1982 to also cover Trident. The Trident missiles rely on the US for maintenance which is done by the manufacturer Lockheed Martin; missiles have to return to the US for scheduled maintenance every few years. The UK also purchases the aeroshells required for producing nuclear warheads from the US.
The US-UK mutual defence agreement which underpins this cooperation – including the missile maintenance – was extended indefinitely in 2024 and includes clauses that make it difficult to terminate the arrangement. However, there is still the risk that the US could decide to ignore the agreement or threaten to do so as a form of leverage.