Boris Johnson is fighting to cling onto his job after being handed a Partygate fine by police over his own birthday bash.
Scotland Yard's decision to fine Mr Johnson makes him the first sitting Prime Minister to be found to have broken the law.
But while Mr Johnson apologised, he made it clear he won't resign for attending the lockdown gathering in Downing Street for his 56th birthday on 19 June 2020.
His future now rests in the hands of Tory MPs, who have to decide whether to oust him or gamble that the furious public will forgive him over Partygate.
The only way to topple a Prime Minister who won't resign is through a no-confidence vote. A ballot is triggered when 54 Conservative MPs - 15% of the parliamentary party - write to Tory backbench chief Sir Graham Brady.
At the height of the scandal in January and February, mutinous Conservative MPs were openly talking about sending no-confidence letters - with a handful breaking cover.
But early indications suggest Conservative MPs are now rallying around the Prime Minister amid concerns about a leadership vacuum during the conflict in Ukraine.
Some MPs are also privately concerned about the lack of an obvious successor. Chancellor Rishi Sunak's leadership hopes were already in tatters after a damaging row over his wife's tax affairs - and he also received a Partygate fine for the same gathering.
Foreign Secretary Liz Truss, another frontrunner, initially won plaudits for her handling of the Ukraine crisis but also caused alarm by her disastrous suggestion the Brits should go to fight in Ukraine.
No10 will be watching carefully to judge the mood of Tory MPs in the coming days.
Tory Nigel Mills became the first to call for the PM to quit today, saying his position had become "untenable". But some of the PM's most vocal critics have fallen in line.
Here are some of the Tories who have retracted their criticism so far...
Douglas Ross
The Scottish Tory leader demanded Boris Johnson resign in January after the PM admitted to briefly attending a BYOB bash in the Downing Street garden in May 2020.
Mr Ross, who quit as a junior minister after Dominic Cummings ' lockdown jaunt to Barnard Castle, was one of the first senior Tories to call on the PM to quit.
But he withdrew his letter to the 1922 Committee last month and said the focus should be on the war in Ukraine.
Mr Ross doubled down on his position despite the news that Mr Johnson had been fined by police.
"Anything that would destabilise the UK Government at this time would be a bonus to Vladimir Putin," he told BBC Radio Scotland.
Sir Roger Gale
Sir Roger Gale publicly confirmed he had submitted a no-confidence letter in January, branding Mr Johnson a “dead man walking”.
The veteran backbencher, who is a long-time critic of the PM, told LBC: "I think it's very serious indeed. And I frankly think that he's done a good job delivering certain things.
“But I think we've now got to the stage where frankly we have to find another leader."
But he has now said it is not the time to unseat the Prime Minister due to the war in Ukraine.
David Davis
The former Brexit Secretary stood up in the Commons in January and quoted the words that helped to oust Neville Chamberlain: “You have sat there too long for all the good you have done. In the name of God, go.”
Mr Davis never said he had submitted a letter but he was openly critical of the Prime Minister over Partygate.
But weeks later he U-turned and told the Evening Standard that "now is not the time to talk about it" after Russia's invasion of Ukraine.
The outspoken MP has kept his counsel since the PM was fined, suggesting he might have more to say.
Andrew Bridgen
A former Johnson ally, Mr Bridgen called on the PM to stand down or risk his legacy becoming "mired in sleaze".
The MP told the Telegraph in January: "If Boris truly loves our country, our democracy and our party he should go now with some semblance of grace."
But he withdrew his letter in March, saying it would be an "indulgence" to hold a leadership contest during the Ukraine conflict.
Mr Bridgen did not repeat his calls for the PM to go after the news of the fines broke, but he warned: "This is not the end of this matter."
