LONDON — Prime Minister Boris Johnson on Saturday suffered a serious new blow at the end of a week of turmoil in British politics when his close ally and negotiator on Brexit, David Frost, announced his resignation, citing differences over the direction of government policy.
Mr. Frost, a member of the cabinet, was a leading architect of the country’s Brexit agreement and was engaged in difficult negotiations with the European Union over how the country’s exit terms applied to Northern Ireland.
In his letter of resignation, Mr. Frost, who is a member of the House of Lords, said that Brexit was “secure” but that the prime minister was aware of his “concerns about the current direction of travel,” hinting at differences over policy since Britain quit the European Union.
He added: “I hope we will move as fast as possible to where we need to get to: a lightly regulated, low-tax, entrepreneurial economy at the cutting edge of modern science and economic change.”
The announcement of his departure, which he said in his letter would be effective immediately, heaps new pressure on Mr. Johnson, whose leadership has been called into question by a succession of recent setbacks just as Britain combats a new wave of coronavirus infections. Mr. Frost’s resignation had been reported earlier in the day by The Mail on Sunday.
Mr. Frost, who according to surveys is very popular among Conservative Party members, also hinted in his letter that he had significant differences with Mr. Johnson over coronavirus restrictions: “We also need to learn to live with Covid and I know that is your instinct too,” he wrote. “You took a brave decision in July, against considerable opposition, to open up the country again. Sadly it did not prove to be irreversible, as I wished, and believe you did too.”
Mr. Frost added that he hoped that the country could get back on track and “not be tempted by the kind of coercive measures we have seen elsewhere.”
The Mail on Sunday said that Mr. Frost had told the prime minister about his decision a week ago.
But the timing of his announcement could scarcely have been worse for Mr. Johnson, coming at the end of a disastrous week. On Tuesday, nearly 100 of his own lawmakers rebelled over government plans to require a pass proving vaccination status or a negative Covid test to enter larger venues.
Then on Friday, Mr. Johnson’s Conservative Party lost a seat it had held for more than a century in an election to replace Owen Paterson, one of its lawmakers, who resigned after breaking parliamentary lobbying rules.
Those events have raised speculation about a challenge to Mr. Johnson’s leadership, though most analysts believe that is unlikely to happen imminently, particularly since Parliament is now in recess for the Christmas holiday.
However, the political situation is volatile with speculation that the government could introduce tougher new coronavirus restrictions to curb the spread of the Omicron variant. The rebellion in Parliament on Tuesday underscored the opposition among Conservative lawmakers to any such moves. But on Saturday, Britain registered more than 90,000 coronavirus cases, and there are growing fears that the country’s overstretched health service could be overwhelmed.
Mr. Frost was one of the most hard-line advocates of Brexit, but, despite his combative stand in talks with the European Union, the government has recently backed away from a threat to suspend part of its agreement on post-Brexit trade terms for Northern Ireland. Britain has also dropped its demand to remove the European Court of Justice as the ultimate arbitrator of trade rules.
Speaking to Times Radio, one Conservative lawmaker, Andrew Bridgen, said that Mr. Frost’s resignation would be a “watershed moment” for many of his colleagues and was a “devastating blow for the government and for the prime minister,” adding that Mr. Johnson must “change or go.”
Jenny Chapman, the Labour Party’s shadow minister of state at the Cabinet Office, said on Twitter that the government was “in chaos,” adding, “the country needs leadership not a lame duck PM whose MPs and cabinet have lost faith in him. Boris Johnson needs to apologize to the public and explain what his plan is for the next few weeks.”