Boris Johnson will face a parliamentary misconduct investigation, after MPs backed a crunch House of Commons motion over his breaches of coronavirus laws.
The Labour motion, which was unopposed by the Government, means the Partygate scandal will be referred to the privileges committee - which can determine whether the Prime Minister's repeated denials of there being any parties in Number 10 during the height of lockdown amounted to a "contempt of the House".
By convention, if a Government minister is found to have misled Parliament they are expected to resign or are usually sacked.
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Tory MPs had initially been ordered to back a Government amendment which would have deferred any decision on referring the matter to the committee until after the conclusion of the Met Police inquiry.
But in a late U-turn shortly before the debate began, Commons Leader Mark Spencer said there would be a free vote for Tory MPs.
It follows speculation at Westminster that Tory MPs were not prepared to back the Government’s attempt to kick the issue into the long grass.
The scale of Tory unease was set out by Hazel Grove MP William Wragg, who confirmed he had submitted a letter of no confidence in Mr Johnson’s leadership.
Mr Wragg said: "I cannot reconcile myself to the Prime Minister's continued leadership of our country and the Conservative Party. I submitted my letter of no confidence to the chairman of the 1922 committee in December of last year."
Mr Wragg told MPs that a turning point for him was the decision to bring forward Covid Plan B measures to "distract" from the furore over Partygate. He said: "I therefore thought to myself if a Government was prepared to bring such measures forward earlier, in order to distract from its own embarrassment, that the Prime Minister was no longer fit to govern."
Former minister Steve Baker, an influential organiser on the Tory benches, said Mr Johnson “should be long gone”.
“Really, the Prime Minister should just know the gig’s up,” Mr Baker, who was a prominent Brexiteer involved in ousting Theresa May, said.
Asked on the first day of his trade mission to India whether he knowingly or unknowingly misled Parliament, Mr Johnson said: “Of course not.”
He told reporters: “I’m very keen for every possible form of scrutiny and the House of Commons can do whatever it wants to do.
“But all I would say is I don’t think that should happen until the investigation is completed.”
Mr Johnson’s aides are braced for him to receive multiple fines, having already been handed one fixed-penalty notice for the gathering on his 56th birthday.
He is thought to have been at six of the 12 events under investigation by Scotland Yard.
The investigation by the privileges committee is expected to begin once all police inquiries have concluded.
