Jack Doyle, Number 10's director of communications, has left his role and is reported to have told staff that recent weeks in Downing Street had "taken a terrible toll on my family life".

News of his departure on Thursday came just hours after another of the prime minister's top aides, Number 10 policy chief Munira Mirza, quit over Mr Johnson's use of a discredited claim that Labour leader Sir Keir Starmer personally failed to prosecute Jimmy Savile.

And, in a triple blow, further pressure was heaped on the prime minister over that row when Chancellor Rishi Sunak - widely touted as a potential successor to Mr Johnson - told reporters: "I wouldn't have said it."

Departing press chief caught up in partygate row

Mr Doyle, a former journalist, joined Mr Johnson's Downing Street team in early 2020 following the Conservatives' general election victory.

He was recently caught up in the partygate scandal afflicting Number 10 when he was reported to have made a speech and handed out awards at an alleged Christmas party in Downing Street in December 2020.

As well as acknowledging the impact of a turbulent few weeks in Number 10 amid the emergence of multiple claims of lockdown breaking in Downing Street, Mr Doyle was also reported on Thursday to have told staff it had always been his intention to only serve in government for two years.

A Number 10 spokesperson said: "Jack Doyle has left government. He has made a huge contribution and the prime minister is immensely grateful for the work he has done."

PM's policy chief leaves over Johnson's 'scurrilous' Savile claim

News of Mr Doyle's departure came not long after it was revealed that Ms Mirza had resigned from her £145,000-a-year role as the prime minister's policy chief.

She cited Mr Johnson's "scurrilous accusation" that Sir Keir was to blame for Savile, a prolific sex offender, not being prosecuted.

In her resignation letter to the prime minister, as published by The Spectator magazine, Ms Mirza wrote: "I believe it was wrong for you to imply this week that Keir Starmer was personally responsible for allowing Jimmy Savile to escape justice.

"There was no fair or reasonable basis for that 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.

"You tried to clarify your position today but, despite my urging, you did not apologise for the misleading impression you gave."

Chancellor distances himself from PM's Savile comments

Mr Sunak, speaking at a Downing Street news conference on Thursday evening, described Ms Mirza as a "valued colleague" who he "very much enjoyed working with".

"I am sorry to see her leave government, I will miss working with her," he said.

Mr Sunak also sought to put distance between himself and the prime minister over the row about the Savile comments.

"With regard to the comments, being honest I wouldn't have said it and I am glad the prime minister clarified what he meant," the chancellor added.

Asked if Mr Johnson should apologise for his remarks, Mr Sunak said: "That's for the prime minister to decide."

PM 'sorry' to see aide depart

Mr Johnson on Thursday night said he was "sorry" see Ms Mirza depart, adding: "She's done an outstanding job and has been a wonderful colleague for a long time."

However, speaking to Channel 5, the prime minister said he didn't agree with her assertion that his Savile comments were "inappropriate and partisan".

"Let me make it absolutely clear, because people keep going on about this, and no-one is commenting, least of all me, about the personal involvement of the leader of the opposition in the handling of that case," Mr Johnson said.

"All that I've said is that the leader of the opposition apologised for the CPS's handling of that issue during his tenure and that's all frankly that needs to be said on that matter."

'This PM is finished'

Ms Mirza has been a longtime ally of the prime minister and previously worked with Mr Johnson when he was London mayor.

Mr Johnson once included Ms Mirza in a list of the five women who had most influenced him.

In her resignation letter, Ms Mirza added: "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."

Dominic Cummings, the prime minister's estranged former chief adviser, praised Ms Mirza's "moral courage".

He added on Twitter: "It's also an unmistakeable signal the bunker is collapsing & *this PM is finished*."

Downing Street swiftly announced that Ms Mirza had been replaced as the head of the Number 10 policy unit by Arundel and South Downs MP, Andrew Griffith, who is a loyal ally of the prime minister.

A Number 10 spokesperson said: "We are very sorry Munira has left Number 10 and are grateful for her service and contribution to government."

What did the PM say about Starmer and Savile?

The row over Mr Johnson's comments about Savile followed his appearance in the House of Commons on Monday.

As he responded to Sir Keir in the Commons, Mr Johnson referred to the Labour leader's former role as director of public prosecutions (DPP).

The prime minister claimed Sir Keir had "spent most of his time prosecuting journalists and failing to prosecute Jimmy Savile, as far as I can make out".

With Mr Johnson's remarks having caused uproar in Westminster, including among some Conservative MPs, Sir Keir later accused the prime minister of making a "ridiculous slur" and of "parroting the conspiracy theories of violent fascists to try to score cheap political points".

The victims of Savile, a prolific sex offender, also demanded Mr Johnson withdraw his comments.

Fact-checking organisations have found that Sir Keir was not personally involved in the CPS decision not to prosecute Savile.