Johnson's finance and health secretaries quit on Tuesday following the latest scandal to hit the government, triggering the departure of around 15 lower-ranking politicians and the withdrawal of support of once loyal lawmakers.
With the tide of resignations rising, some questioned whether the prime minister could fill the vacancies.
Johnson, due to appear in the House of Commons lower house of parliament for his weekly political questions at midday, sought to reassert authority by quickly appointing Nadhim Zahawi as finance minister.
But as former education secretary Zahawi toured broadcast studios on Wednesday morning to set out the government's priorities, he was confronted with news of fresh resignations.
Solicitor General Alex Chalk, the government's second-most senior legal adviser, said the cumulative effect of a series of scandals meant the public no longer believed the government could uphold expected standards of candour.
"I regret that I share that judgment," he said.
The level of hostility Johnson faces within his party will be laid bare when he appears in parliament for the question session, and before the chairs of select committees for a scheduled two-hour grilling later on Wednesday.
"I suspect we will have to drag him kicking and screaming from Downing Street," one Conservative lawmaker told Reuters, speaking on condition of anonymity. "But if we have to do it that way then we will."
Johnson, a former journalist and London mayor who became the face of Britain's departure from the European Union, won a landslide election victory in 2019 before taking a combative and often chaotic approach to governing.
His leadership has been mired in scandals and missteps over the last few months, with the prime minister fined by police for breaking COVID-19 lockdown laws and a damning report published about the behaviour of officials at his Downing Street office who breached their own lockdown rules.
There have also been policy U-turns, an ill-fated defence of a lawmaker who broke lobbying rules, and criticism he has not done enough to tackle a cost-of-living crisis, with many Britons struggling to cope with rising fuel and food prices.
The Times of London newspaper said Johnson's "serial dishonesty" was "utterly corrosive" of effective government.
"Every day that he remains deepens the sense of chaos," it said. "For the good of the country, he should go."
The latest scandal saw Johnson apologising for appointing a lawmaker to a role involved in party welfare and discipline, even after being briefed that the politician had been the subject of complaints about sexual misconduct.
Downing Street's narrative changed several times over what the prime minister knew of the past behaviour of the politician, who was forced to resign, and when he knew it. His spokesman blamed a lapse in Johnson's memory.
That prompted Rishi Sunak to quit as chancellor of the exchequer - the finance minister - and Sajid Javid to resign as health secretary, while others left their junior ministerial or envoy roles.
"It is clear to me that this situation will not change under your leadership - and you have therefore lost my confidence too," Javid said in his resignation letter.
A snap YouGov poll found 69 per cent of Britons thought Johnson should step down as prime minister but for the time being the remainder of his top ministerial team offered their backing.
A month ago, Johnson survived a confidence vote of Conservative lawmakers, and party rules mean he cannot face another such challenge for a year.
However, some lawmakers are seeking to change those rules, while he is also under investigation by a parliamentary committee over whether he lied to parliament about COVID-19 lockdown breaches.
"After all the sleaze, the scandals and the failure, it's clear that this government is now collapsing," Labour leader Keir Starmer said.
