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The UK and France have pledged for the first time to co-ordinate the use of their nuclear weapons, saying they would jointly respond to protect Europe from any “extreme threat”.
The announcement by Prime Minister Keir Starmer and Emmanuel Macron, during a state visit by the French president to Britain, marks a significant step-up in co-operation between Europe’s two nuclear powers as they seek to respond to a growing threat from Russia.
It also comes as President Donald Trump has cast doubt on US commitment to collective defence on the continent, prompting interest in some European countries, including Germany, for London and Paris to extend their nuclear umbrella.
The UK government said on Wednesday the agreement with France meant “for the first time that the respective deterrents of both countries are independent but can be co-ordinated”.
“There is no extreme threat to Europe that would not prompt a response by both nations,” the UK added. “As such, any adversary threatening the vital interests of Britain or France could be confronted by the strength of the nuclear forces of both nations.”
An Élysée Palace official said the step-up “was a message both to our allies and our adversaries” since it enacted a “solidarity between two nuclear powers”.
While the UK is a member of Nato’s nuclear planning group and commits its arsenal to the defence of the security alliance, France has long fiercely guarded its independent, sovereign decision-making on nuclear weapons.
Paris does not take part in the Nato nuclear-sharing agreement under which the US stations its weapons in Europe and allows several European countries to carry them in fighter jets.
The UK’s current nuclear deterrent consists of submarine-launched missiles, which are acquired from the US but can be operated independently.
London recently announced plans to add an air-launched option for the first time in decades, with plans to buy American F-35A jet fighters that could deliver US-made nuclear weapons.
France’s nuclear deterrent is entirely homegrown and consists of both submarine-launched and air-launched weapons.
In a speech to the UK parliament on Tuesday, Macron said the UK and France had a “special responsibility” for the security of Europe.
“There is an expectation in Europe that, faced with revisionist neighbours, our two countries have a special responsibility for the security of the continent,” he said. “And it is time to articulate it.”
Macron has maintained the nuclear doctrine set by France for decades that its “vital interests” — the factors that determine the use of nuclear weapons — have a “European dimension”.
But Paris never defined the term, so as to keep the president’s options open and the adversary guessing, the key to all nuclear deterrence.
The UK and France have precedent for signalling expanded deterrence. In 1995, Britain and France said in the so-called Chequers declaration that they could not envisage a situation in which “the vital interests of either of our two countries . . . could be threatened without the vital interests of the other being also threatened”.
Camille Grand, a former senior Nato official who is now at the European Council on Foreign Relations think-tank, said the announcement represented a “meaningful change” in the nuclear doctrines of the two allies, and one that could lead to closer operational co-ordination, such as on submarine patrols.
“It is a quite powerful statement of the Franco-British commitment to European security,” he said. “This is also important since the UK and France both have comparatively small nuclear arsenals, which makes co-ordination desirable.”
Lawrence Freedman, emeritus professor of war studies at King’s College London, said: “As far as I know, the French have never admitted publicly that they co-ordinate nuclear capabilities with anybody else, so that in itself is quite an important development.”
Potential co-operation might involve coordinating refits of nuclear submarines in such a way as to have as many at sea at any time as possible, he added.
In addition to the announcements on nuclear weapons, the UK and France were set to sign the “Lancaster House 2.0 declaration”, an update of a broad-ranging defence pact agreed in 2010.
It includes plans to build a new generation of long-range missiles to eventually replace the Storm Shadow/Scalp that has proven highly effective in the hands of Ukraine, and expand a joint Franco-British expeditionary force.
The UK said the two countries would also jointly develop next-generation air-to-air missiles, high-tech microwave weapons and jammers for downing drones and missiles, and on using artificial intelligence to improve synchronised strike capabilities.
Additional reporting by Charles Clover in London
