Britain has been told by experts it needs to prioritise expanding its nuclear arsenal, warning "urgent action is needed". They suggest the UK should look at diversifying its nuclear strike capabilities, with the Royal Navy’s ageing Vanguard-class submarines currently the only way Britain can carry out such attacks, if required.

In a column in The Spectator, journalist and author Paul Mason, senior lecturer Marc De Vore and think tank co-director James Rogers painted a concerning picture over the state of the UK and Europe’s nuclear capabilities. The experts said the pending publication of the Strategic Defence Review (SDR) must "take seriously" evidence from those who have argued Britain’s nuclear deterrent might not be up to scratch, warning "the threat is real" and the UK is now facing a "twofold" problem. They explained how Russia and China’s growing "sub-strategic" nukes, which would cause a smaller nuclear explosion, gives the nations "an escalation ladder".

In contrast, the UK - which lacks this capability - only has an "on-off switch" with its Trident nuclear deterrent, they warned.

They wrote this would be fine if the US, which has also developed sub-strategic nuclear weapons, were a "100% reliable ally" but warned this is no longer the case under the Donald Trump administration as concerns continue over Washington commitment to European security.

The US provides a nuclear umbrella for Europe, with the UK and France the only nuclear powers on the continent.

Germany’s new Chancellor Friedrich Merz previously said he wants to speak to France and Britain about sharing nukes.

Unlike the UK, France can launch nuclear strikes from fighter jets, as well as submarines.

In The Spectator, Mason, De Vore and Rogers argued Britain could make a formal commitment to use Trident missiles for collective defence of European allies beyond agreements in NATO.

However, they warned for this to be "credible", then "the technical form of the deterrent may have to change".

They said: "The Vanguard submarines are, of course, capable of firing a single missile with a small warhead in response to a 'tactical' strike by Russia. But there are two risks associated with such a move: first, that Russia interprets the launch as a strategic strike and responds accordingly; second, that it gives away the position of the submarine firing it – requiring us to keep two submarines at sea, not one.

"Logic, therefore, points to the UK acquiring more diverse ways of delivering a nuclear strike, and altering its doctrine to allow for the use of what the French call 'theatre-level' nukes."

Their words echo those made by a top defence expert last month, who suggested one option could be equipping the Storm Shadow missile, used by the RAF, with a low-yield warhead.

They wrote: "Few of us would willingly add to the world’s arsenal of mass destruction. But the asymmetry between the threat and our defences against it are so strong that urgent action is needed."

The experts added that following the publication of the long-awaited SDR, the Government should look for a cross-party agreement to look towards developing sub-strategic nukes.