British Prime Minister Boris Johnson suffered four staff defections on Thursday as pressure intensified on the embattled leader over lockdown parties and his loose-lipped style of politics.

One of the departures was linked to an inflammatory remark made by Johnson, attacking opposition Labour leader Keir Starmer over a notorious paedophile.

"Being honest, I wouldn't have said it and I'm glad the prime minister clarified it," finance minister Rishi Sunak said in an extraordinary rebuke of his boss during a televised news conference.

Sunak is tipped as a leading contender to replace Johnson, if a brewing Conservative revolt against the prime minister develops further.

Downing Street confirmed that chief of staff Dan Rosenfield was leaving, just over a year after he took on the role with a brief to professionalise Johnson's chaotic operation.

His resignation comes after a top civil servant, in a long-awaited inquiry, this week condemned "failures of leadership" in Downing Street over a series of parties held in violation of Covid restrictions.

Munira Mirza quit on Thursday
Munira Mirza quit on Thursday as head of Prime Minister Boris Johnson's policy unit Photo: AFP / Tolga Akmen

Also going is Johnson's "principal private secretary", Martin Reynolds, who sent a now-notorious email in May 2020 urging Downing Street staff to "bring your own booze" to one lockdown gathering.

Johnson "thanked them both for their significant contribution to government and No 10, including work on the pandemic response and economic recovery", a spokesperson said.

Their departures were confirmed not long after those of two other top advisors -- director of communications Jack Doyle and head of policy Munira Mirza.

According to the Daily Mail, Doyle told colleagues as he left: "It was always my intention to do two years. Recent weeks have taken a terrible toll on my family life."

Doyle was implicated in the "partygate" affair after attending at least one Downing Street event that is under investigation by police.

Johnson's long-term ally Mirza quit after the prime minister tried to link Labour's Starmer to the failure by UK authorities to prosecute veteran TV host Jimmy Savile, who died in 2011 aged 84.

Downing Street chief of staff Dan Rosenfield
Downing Street chief of staff Dan Rosenfield is resigning after just over a year in the post, one of four aides to desert embattled Prime Minister Boris Johnson on Thursday Photo: AFP / Niklas HALLE'N

While alive, Savile was seen as a widely loved presenter. But after his death accusations emerged that he had been a serial abuser of hundreds of children, without facing prosecution.

In parliament on Monday, Johnson shocked many on his own side when he aired a conspiracy theory prevalent among far-right groups that Starmer had personally failed to prosecute Savile when he was director of state prosecutions in England and Wales from 2008 to 2013.

Under Starmer's watch, police decided not to press charges against Savile despite widespread suspicions about his behaviour.

Starmer was not personally involved in the decision, and he accused Johnson of "parroting the conspiracy theories of violent fascists to try to score cheap political points".

Johnson belatedly tried to backtrack late Wednesday, after strong criticism from some Tory MPs, sections of the media and a lawyer representing victims of Savile.

But Mirza said that did not go far enough, according to her resignation letter reported by the Spectator magazine.

Johnson's remark in parliament "was an inappropriate and partisan reference to a horrendous case of child sex abuse", she said, noting that the prime minister had yet to apologise.

"You are a better man than many of your detractors will ever understand, which is why it is so desperately sad that you let yourself down by making a scurrilous accusation against the leader of the opposition."

Mirza, who was once a member of the now-defunct Revolutionary Communist Party, worked with Johnson when he was mayor of London from 2008 to 2016, joining him in Downing Street from 2019.

Speaking to Channel 5 News on Thursday before news broke of the other resignations, Johnson said he was "sorry to lose" Mirza, crediting her for "an outstanding job".

Dominic Cummings, Johnson's former chief aide turned bitter foe, said Mirza's resignation was an "unmistakable signal the bunker is collapsing" as the "partygate" allegations swirl.

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