The warning by Richard Goldberg, until last week a member of the White House national security council (NSC), highlights the dilemmas UK foreign and defence policymakers will face as Britain tries to steer its own course between Washington and Brussels after Brexit.

Goldberg told the BBC: “The question for prime minister Johnson is: ‘As you are moving towards Brexit, as your supporters of Brexit really do not like the nuclear deal, want you to get out of the nuclear deal … what are you going to do post-31 January as you come to Washington to negotiate a free-trade agreement with the United States?’”

Goldberg, who was in charge of countering Iranian weapons of mass destruction at the NSC, said: “It’s absolutely in his interests and the people of Great Britain’s interests to join with President Trump, with the United States, to realign your foreign policy away from Brussels, and to join the maximum pressure campaign to keep all of us safe.”

He made his remarks after France, Germany and the UK agreed to put the Iran deal into its dispute-resolution mechanism, the first step towards an eventual European withdrawal from the deal. But the three European countries stressed the move was designed to persuade Iran back into compliance and rescue the deal from collapse.