4 senior aides to Boris Johnson resign from No. 10

British Prime Minister Boris Johnson. [Reuters]

Four of British Prime Minister Boris Johnson's closest aides resigned on Thursday and his finance minister criticised him over a barb he made about the main opposition leader, in a tumultuous day for his government.

Johnson's premiership is facing a growing crisis in the wake of 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.

On Thursday, his Chief of Staff Dan Rosenfield, his Principal Private Secretary Martin Reynolds, his Director of Communications Jack Doyle and his head of policy Munira Mirza all resigned.

Three of the officials were directly linked to the Downing Street gatherings and two senior Conservatives said it looked like the start of a reset in Johnson's administration.

Johnson's office said Rosenfield and Reynolds would remain in their posts for the time being.

Earlier this week, Johnson promised an overhaul of his Downing Street operation after a report criticised "serious failures of leadership" over a series of gatherings that were held there during Covid-19 lockdowns.

Amid plummeting popularity ratings and open calls for his resignation from some of his own lawmakers, Johnson has also been condemned for accusing Labour Party leader Keir Starmer of failing to prosecute Jimmy Savile, one of Britain's worst sex offenders, during his time as Director of Public Prosecutions.

The false 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 prompted 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."

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 from some Conservative lawmakers after a report on Monday found that parties had taken place at his Downing Street office and residence while social mixing was all but banned, gatherings which police are also investigating.