Johnson's leadership is facing a growing crisis amid anger over a series of alcohol-fuelled parties held at his Downing Street office and residence during coronavirus lockdowns, a scandal which followed a series of other missteps
The latest controversy erupted when during angry exchanges in parliament on Monday, Johnson accused Labour Party leader Keir Starmer of failing to prosecute Jimmy Savile, one of the country's worst sex offenders, during his time as Director of Public Prosecutions.
The claim, which Starmer said amounted to Johnson "parroting the conspiracy theories of violent fascists," has angered not only opponents but also some within his own party.
Johnson has declined to apologise but did back down from the comments on Thursday.
However, it was not enough to stop Munir Mirza, his head of policy who had worked with him for 14 years, to quit her job and also provoked criticism from finance minister Rishi Sunak.
Asked whether the prime minister should have apologised, Sunak, considered the leading contender to replace Johnson should he be forced out, said: "Being honest, I wouldn't have said it, and I am glad the prime minister clarified what he said."
Savile, a celebrated TV and radio host, was never prosecuted despite a number of police investigations and warnings about his conduct.
After his death in 2011 at age 84, it was revealed Savile had abused hundreds of victims, the youngest of whom was just eight.
Starmer, who headed the Crown Prosecution Service at a time when Savile was being investigated, had no direct involvement in the case but did later apologise for the failings.
In interviews on Thursday, Johnson tried to back down from his original comments which provoked scorn not just from opponents but some in his own Conservative party.
"I want to be very clear about this because a lot of people have got very hot under the collar," Johnson told broadcasters.
"I'm talking not about the leader of the opposition's personal record when he was... DPP and I totally understand that he had nothing to do personally with those decisions."
But Mirza said there had been no fair or reasonable basis for his original assertion.
"This was not the usual cut and thrust of politics; it was an inappropriate and partisan reference to a horrendous case of child sex abuse," The Spectator magazine cited Mirza as saying in a letter to Johnson.
"I hope you find it in yourself to apologise for a grave error of judgement made under huge pressure... It is not too late for you but, I'm sorry to say, it is too late for me."
Johnson said he was sorry to lose Mirza but rejected her assessment that his Starmer comments were inappropriate.
"Well I don't agree with that," he told 5 News.
To compound his woes, his Director of Communications Jack Doyle, considered one of his inner circle, also left the government on Thursday.
However, the Daily mail reported his departure was not connected to Mirza's resignation.
Johnson is trying to weather the gravest threat to his leadership with his ratings plummeting and the Conservatives falling well below Labour in opinion polls.
He faced renewed calls to resign after a report on Monday concluded that parties had taken place at Downing Street while COVID-19 lockdown rules were in force, gatherings which police are also investigating.
The report pointed to "serious failures of leadership" at the heart of the British government.
Opposition figures have called him a habitual liar who has misled parliament - accusations he has brushed aside.
