Scottish Conservative leader Douglas Ross has called for Boris Johnson to resign after the prime minister admitted attending a Downing Street party during lockdown.
Mr Johnson apologised about the May 2020 gathering while claiming that it was “technically within the rules”.
He said he “believed implicitly that this was a work event” at the time.
But Mr Ross – who is an MP as well as an MSP – said the prime minister’s position was “no longer tenable”.
The Scottish Tory leader said he had a “difficult conversation” with Mr Johnson on Wednesday afternoon, and that he would write to the 1922 Committee to register his lack of confidence in his leadership.
He said: “He is the prime minister, it is his government that put these rules in place, and he has to be held to account for his actions.”
Mr Johnson faced calls to quit from opposition parties during prime minister’s questions, after admitting for the first time that he attended the event.
This came two days after an email was leaked to ITV News in which 100 staff were invited to a “bring your own booze” event in the Downing Street garden, at a time when government guidance was to not meet up with more than one person from another household.
Mr Johnson said he was present for 25 minutes, adding: “With hindsight I should have sent everyone back inside.
“I should have found some other way to thank them, and I should have recognised that – even if it could have been said technically to fall within the guidance – there would be millions and millions of people who simply would not see it that way.”
Mr Ross said he believed Mr Johnson was “genuine” in his apology, but that “it was wrong to attend the event”.
He added: “Crucially for me he said that in hindsight if he had his time again he would have done things differently
“To me that is an acceptance from the prime minister that he did wrong, and therefore to be consistent with what I’ve said before I don’t believe his position as prime minister and leader of the Conservative Party is tenable and he does need to resign.”
The majority of Scottish Conservative MSPs quickly backed Mr Ross, with Murdo Fraser saying that the prime minister had “lost public trust, and in the interests of the country and the Conservative Party he should step down”.
Douglas Ross once endorsed Boris Johnson for the top job in UK politics, but he later resigned from government over the prime minister’s failure to dismiss Dominic Cummings for his travels during lockdown.
Since then, Mr Ross – who is also a football referee – has occasionally raised the political equivalent of a yellow card to the PM.
Now he’s showing him a red, describing his position as “untenable” for attending a bring-your-own-booze event in the Downing Street garden.
In that call, he has overwhelming backing from his MSP group – as he becomes the first Scottish Tory leader to effectively front a campaign to oust his UK party leader.
He must now have everything crossed that Boris Johnson is actually forced from office and he’s not stuck with a leader he has so publicly rejected.
Mr Ross’s predecessor as Tory leader, Jackson Carlaw, said Mr Johnson had “lost the confidence of the country”, while another former leader, Baroness Ruth Davidson, said Mr Ross had made “the right call”.
But some Tory MPs rallied behind the prime minister, with Sir Christopher Chope saying he had “never heard such an abject apology” in his time in parliament, which he believed it was “genuinely sincere”.
The SNP has been calling for Mr Johnson’s resignation for some time, with First Minister Nicola Sturgeon saying on Wednesday that “the office of prime minister would be greatly enhanced by Boris Johnson’s departure from it”.
And Labour leader Sir Keir Starmer said Mr Johnson should “do the decent thing and resign” after “months of deceit and deception” about parties during lockdown.
Mr Johnson – who has urged opponents to wait for the conclusions of an internal review – toured the Commons tea rooms after prime ministers questions in an attempt to shore up support among his backbenchers.
If 54 MPs send letters to the 1922 committee – an influential group of backbench Tories – it would trigger a formal challenge to his leadership of the party.
So far Mr Ross and Sir Roger Gale are the only MPs who have confirmed they will do so, although the process is theoretically confidential.
Mr Ross said this was a “course of action open to MPs”, but said he did not speak on behalf of all Conservatives.
He added: “I explained to the PM today that I felt he should stand down because of this, but that is ultimately his decision.”
Timeline: The alleged government gatherings
The government is facing mounting pressure over several events that are alleged to have been held during lockdowns in 2020. Here is what we know about them and the restrictions in place at the time:
Boris Johnson announced a plan to take the “first careful steps” out of the lockdown that began in March 2020. But he said people should continue to “obey the rules on social distancing and to enforce those rules we will increase the fines for the small minority who break them”.
Legal restrictions at the time said you could not leave your house without a reasonable excuse and government guidance was that you could meet one person outside of your household in an outdoor setting while exercising.
A photo from May 2020 showed the prime minister and his staff with bottles of wine and a cheeseboard in the Downing Street garden. When asked about it, Boris Johnson said, “those people were at work talking about work”.
About 100 people were invited by email to “socially distanced drinks in the No 10 garden” on behalf of the prime minister’s principal private secretary, Martin Reynolds.
Witnesses told the BBC the PM and his wife were among about 30 people who attended.
Boris Johnson has confirmed he attended the event, saying he was there for 25 minutes and “believed implicitly that this was a work event”.
Boris Johnson announced plans for a “significant return to normality” in England by Christmas “through targeted, local action” instead of national lockdowns.
But he added that the timetable relied on “every one of us staying alert and acting responsibly”.
With cases of coronavirus rising again, the prime minister told people in England that “we are once again asking you to stay at home” as a new national lockdown began.
He said people should only leave their homes “for work if you can’t work from home, for education, and for essential activities and emergencies”. Indoor gatherings with other households were banned, unless they were for work purposes.
Sources told the BBC that Downing Street staff members attended a gathering with Carrie Johnson in the flat where she and the prime minister live. A spokesman for Mrs Johnson denies the party took place.
A leaving event was held for No 10 aide, Cleo Watson, where people were drinking, and Mr Johnson made a speech, according to sources.
The second national lockdown ended after four weeks but Boris Johnson replaced those restrictions with “tough tiers to keep this virus down”.
London was placed in tier two, which banned two or more people from different households from meeting indoors, unless “reasonably necessary” for work purposes.
The Department for Education has confirmed it had an office gathering to thank staff for their work during the pandemic. It says drinks and snacks were brought by those who attended and no outside guests or support staff were invited.
The Conservative Party has admitted that an “unauthorised gathering” took place at its HQ in Westminster. It was held by the team of the party’s London-mayoral candidate, Shaun Bailey, who has since stepped down as chair of the London Assembly police and crime committee. The Metropolitan Police is to speak to two people who attended the party.
Multiple sources have told the BBC there was a Christmas quiz for No 10 staff last year. A photo – published by the Sunday Mirror – showed Boris Johnson taking part and sitting between two colleagues in No 10. Mr Johnson has denied any wrongdoing.
London moved into the highest tier of restrictions and Matt Hancock, who was health secretary at the time, said it was important “everyone is cautious” ahead of the festive period.
The Department for Transport apologised after confirming reports of a party in its offices that day, calling it “inappropriate” and an “error of judgment” by staff.
Downing Street originally denied a report by the Daily Mirror that a party took place in Downing Street.
However, a video obtained by ITV News showed the prime minister’s then-press secretary Allegra Stratton, joking about reports of an event, saying: “This fictional party was a business meeting and it was not socially distanced.”