Although Ms Truss backed Remain during the 2016 EU referendum, she has since worked on post-Brexit trade deals as International Trade Secretary and is thought to be ideologically aligned with Lord Frost on the Right of the Conservative Party.

Chris Heaton-Harris, a former chair of the European Research Group of Brexiteer MPs, was moved from the Department of Transport to Ms Truss’ department, where he takes the role of Europe minister.

Ms Truss’s appointment was “noted” on Twitter by Maroš Šefčovič, her opposite number in the EU.

“My team and I will continue to cooperate with the UK in the same constructive spirit on all important tasks ahead, including the Protocol on Ireland/Northern Ireland,” he said.

One official said Lord Frost’s departure had come “totally out of the blue” but admitted he had “frustrations on various fronts”, including over Downing Street’s decision to abandon the UK’s red line on the ECJ operating in Northern Ireland.

Simon Hoare, the chairman of the Northern Ireland affairs committee, told BBC Radio 4’s The World This Weekend that the issues cited by Lord Frost were the same that had been raised by “at least one potential leadership candidate”.

And he said: “I do just wonder whether he’s acting as a bit of an outrider for them, I’m just not sure.”

The move was reported on Saturday night, creating a further headache for the Prime Minister after weeks of discontent over the handling of the Owen Paterson sleaze allegations, “Plan B” Covid restrictions and the loss of the North Shropshire by-election.

Mr Johnson is now facing calls for a reorganisation of his Cabinet and team of No10 officials, amid accusations that Declan Lyons, his political secretary, and Dan Rosenfield, his chief of staff, lack the political experience to fend off attacks.

On Sunday it was also reported that Mark Spencer, the Chief Whip, and Jacob Rees-Mogg, the Leader of the House, could lose their jobs as part of a wider New Year “reset”.

Although Mr Spencer has been blamed for the Government’s mismanagement of the sleaze saga and recent rebellions on the Tory back benches, friends of the Chief Whip last night said he had become a “scapegoat”, and blamed “policy direction and sense of drift” for unease in the Conservative ranks.

At least one more Conservative MP is planning to submit a letter of no confidence in the Prime Minister to the 1922 Committee this week.