LONDON (BLOOMBERG) - Hours after one of Mr Boris Johnson's longest-standing allies quit - with a stinging rebuke of his judgment - the British prime minister gathered shell-shocked staff in Downing Street to tell them "change is good".

But while Mr Johnson has tried to put his trademark optimistic spin on yet another week of turmoil, the ebullient persona that carried him to the top is now jarring with the reality of a desperate battle to cling to power.

He started the week with a plan to reinvigorate his premiership, marked by key announcements to flesh out his key electoral promise to "level up" forgotten communities, make the most of Brexit and tackle a cost-of-living crisis.

Instead, he has been dragged to the brink after a senior civil servant criticised leadership failures over parties, which the police are still investigating, held in his office during the coronavirus pandemic.

The Daily Mirror reported on Friday (Feb 4) that the police have a photograph of Johnson holding a can of beer at his birthday party during lockdown in June 2020.

In the fallout, three other senior aides also left government and more Conservative Members of Parliament (MPs) called on Mr Johnson to resign.

Most ominously, key ministers suddenly appear less willing to give Mr Johnson their full backing.

Both Chancellor of the Exchequer Rishi Sunak and Health Secretary Sajid Javid declined to defend the Prime Minister after he invoked infamous child sex abuser Jimmy Savile during a heated exchange in Parliament over the party allegations with opposition leader Keir Starmer.

According to a front page report in Saturday's edition of the Times, Mr Johnson's Cabinet is in "civil war".

"It's very hard to see how Boris Johnson can re-establish the dominant position in politics that he had a few months ago," Mr David Lidington, who served as former prime minister Theresa May's de-facto deputy, said in an interview Friday.

"They've been shambolic in how they've handled this, and I don't see any sign that this is likely to improve."

Mr Johnson's decision to falsely accuse Mr Starmer, a former director of public prosecutions, of allowing Savile to evade justice before his death in 2011 backfired spectacularly, and bolstered the sense that the crisis engulfing the premier is largely of his own making.

It also robbed Mr Johnson of the chance to brand the departure of senior aides on Thursday as a reset of his Downing Street operation.

His office said the resignations of his chief of staff, communications director and principal private secretary were pre-planned and mutually agreed.

Yet the exit of Ms Munira Mirza, the head of his policy unit and a close aide who has been at his side since he was Mayor of London in 2008, blindsided Mr Johnson. In a further blow, she blamed his "scurrilous" attack on Starmer.

One minister in Mr Johnson's government, who asked not to be identified, said the departure of senior aides had left Mr Johnson looking abandoned and without direction - even if some moves had been planned.

Among Conservative MPs, the focus is increasingly on potential challengers to Mr Johnson. Mr Sunak raised eyebrows when he declared during a televised press conference that he "wouldn't have said" Johnson's Savile comment.

On Friday, Mr Javid pointedly defended Mr Starmer's record when asked about the remark.

The question for the Tories - and Mr Johnson - is whether those they regard as having their eye on the top job, including Foreign Secretary Liz Truss, will continue to wait, or decide that delaying risks damaging their chances.

Mr Johnson would face a vote on his leadership if 15 per cent of his backbenchers - 54 MPs - submit letters calling for his resignation.

At least 14 have so far publicly called on him to resign or said they've lost confidence in him, while the tally of letters is kept secret.

But as many Tory MPs have said they will wait for the police to finish their probe into the so-called partygate scandal or to see if Mr Johnson delivers on a pledge to change his ways, some think it may take a senior figure making a move for the threshold to be reached.

One person familiar with the matter said some MPs are waiting to submit a letter until they are sure Johnson will lose a no-confidence vote.

A public denouncement of Mr Johnson carries risks for challengers.

It would be seen as a betrayal by grassroots Conservative Party members - who ultimately elect the leader and many of whom have a strong affection for the current prime minister.

In the meantime, Mr Johnson is battling on.

He installed former Sky executive and backbench MP Andrew Griffith as his new policy chief, and promised rank-and-file Tory lawmakers more influence.

Several MPs elected in 2019 told Bloomberg they are glad to see him taking action. Yet the chaos is growing just as Mr Johnson faces looming real-world problems beyond Westminster, including tensions with Russia over Ukraine.

The looming squeeze on living standards alone would be too much for a government to survive, even without the partygate fallout, according to Ms Bronwen Maddox, director of the Institute for Government think-tank.

"He's done all this other stuff on top, self-inflicted mistakes which have got people really furious," she said. "It's very, very hard to come back from this."