The political crisis engulfing British Prime Minister Boris Johnson has deepened with the resignation of a close ally, Brexit minister David Frost, who cited pandemic restrictions and the government’s “direction of travel.”

Frost has been handling Britain’s post-Brexit negotiations with the European Union. Frost voiced his dissatisfaction with the government’s policies in a speech last month, saying he was worried Britain wasn’t taking advantage of its exit from the EU to chart a new course of limited government, lower taxes and reduced regulation.

In his resignation letter Saturday, Frost returned to the same theme, saying, “You know my concerns about the current direction of travel. 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.”

He added his frustrations with renewed pandemic curbs, saying, “We also need to learn to live with Covid and I know that is your instinct too. 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. I hope we can get back on track soon and not be tempted by the kind of coercive measures we have seen elsewhere.”

Frost’s departure bookends seven days of enormous setbacks for Johnson. Last week, Johnson faced one of the most significant parliamentary rebellions in modern British history. More than 100 of his Conservative lawmakers voted against the reimposition of tough pandemic restrictions and the introduction of new ones, including vaccine passports to enter nightclubs and venues hosting large events.

The embattled prime minister was further rocked by a humiliating parliamentary by-election defeat in a seat in the English Midlands that the Conservatives had held continuously since 1832.

The resignation of Frost, a former diplomat who was ennobled last year by Johnson so he could join the Cabinet, will likely embolden the sizable libertarian wing of the party already furious over the British leader’s handling of the pandemic.

Conservative rebels are determined to dissuade Johnson from tightening pandemic restrictions even more. On Sunday it emerged Johnson was coming under mounting pressure from the government’s scientific and medical advisers to follow the Netherlands and order a national lockdown ahead of the Christmas holiday.

Advisers have called for an “immediate” curtailment of indoor mixing of households to combat the quickening pace of the omicron variant of the coronavirus. Officials say Johnson has no choice but to consider a range of further measures, ranging from new social distancing rules to a full lockdown, which, if ordered, would be third since the pandemic struck.

Earlier this month, Frost had informed Johnson he was leaving but was persuaded to delay his announcement until January. But Frost’s plan was leaked, forcing him to quit with immediate effect. 

Frost’s departure adds to the disarray in Conservative ranks. Rebellious Conservative lawmakers voiced their worries Sunday about Frost’s resignation. Theresa Villiers, a former Northern Ireland secretary, said it was “very worrying.” Lawmaker Geoffrey Clifton-Brown said it was a “further hammer blow to the PM.”

Conservative insiders say a bid to oust Johnson as party leader, and consequently as prime minister, will unlikely be mounted in the immediate weeks, but some believe he has been “fatally wounded” and Frost’s resignation adds to that perception. It will also complicate in the near term the politics in the Cabinet about what the government should do about rapidly rising coronavirus infections.

The Cabinet is split with some key ministers opposing the reimposition of any more pandemic rules. The opponents include two key ministers, the chancellor, Rishi Sunak, and the foreign secretary, Liz Truss. Both are reported to harbor leadership ambitions.

Even Johnson’s supporters acknowledge he’s now battling the biggest crisis of his tumultuous premiership. But they say Johnson has time to correct his position as the party factions baying for his head are divided about whom they should back to replace him. Johnson loyalists also say that if omicron turns out to be milder than previous variants, he may still weather the storm of the last few weeks.

But many of Johnson’s problems are due to unforced errors that are enraging voters, say his critics. And they see no end in sight while he remains in office to the toxic mix of scandal, government chaos and abrupt policy reversals that are upsetting the electorate.

Vengeful allies of his predecessor in Downing Street, Theresa May, whom he helped to oust, are circling and are keen to topple him. They — as well as the libertarian wing of the party — have seized on last week’s by-election defeat in North Shropshire, which saw a 34 percent swing away from the Conservatives, one of the biggest since the Second World War.

Many voters in North Shropshire said in the days leading up to the ballot that they had been infuriated by recent revelations about lockdown-busting parties in Downing Street last December, at a time the rest of the country was banned from participating in social gatherings and thousands of Britons were prohibited from visiting elderly relatives or family members dying in hospital wards from the COVID-19 disease.

Johnson’s showmanship, once widely seen as an attribute, has also been misfiring as the public mood sours. Last month, a rambling speech at a conference of the country’s top business leaders led to widespread criticism. Johnson lost his notes, had to apologize for losing his way and extensively praised an amusement park, known as Peppa Pig World. He also compared himself to Moses and imitated the noise of an accelerating sports car.