Cabinet ministers have pledged their support for Boris Johnson, as he faces calls to resign after admitting attending a drinks party in lockdown.
Meanwhile, the PM cancelled a visit to Lancashire after a family member tested positive for coronavirus.
Scottish Tory leader Douglas Ross and other senior backbenchers have urged him to stand down.
But cabinet ministers have urged MPs to wait for the outcome of an inquiry into alleged Covid-rule breaking at No 10.
And Commons leader Jacob Rees-Mogg dismissed Mr Ross as a “lightweight”.
Mr Ross has written to the 1922 Committee, which oversees Tory leadership contests, to say he has no confidence in the prime minister.
If 54 or more of the party’s MPs do so, a vote of confidence in Mr Johnson can go ahead – and if he loses, a leadership contest takes place. The chairman of the 1922 committee, Sir Graham Brady, does not reveal how many letters he has received until they have reached the threshold.
Northern Ireland Secretary Brandon Lewis told BBC Breakfast he “absolutely” backed Mr Johnson, adding: “You’ve got to let these investigations get to the full details and the full facts.”
Foreign Secretary Liz Truss said she stood behind the prime minister “100%”, while Chancellor Rishi Sunak said Mr Johnson had been “right to apologise”, adding that he supported his call for “patience” while senior civil servant Sue Gray completes her investigation.
Deputy Prime Minister Dominic Raab said the PM he had given a “very clear account” of what happened and Health Secretary Sajid Javid said “most people have accepted” the need to wait for Ms Gray’s findings.
In the Commons, Mr Rees-Mogg said a future full inquiry into the pandemic would look at whether Covid restrictions had been “proportionate” or “too hard on people”.
“I think everybody understands, on all sides of the House, that people were obeying the rules, and these rules were very hard for people to obey,” he added.
Mr Johnson’s planned visit on Thursday to a vaccination clinic in Lancashire was cancelled and he will follow official guidance, including taking daily tests and limiting contact with other people, a Downing Street spokesperson said.
Downing Street party row
- ANALYSIS: What was really going on in No 10 during lockdown?
- LAURA KUENSSBERG: What next for Johnson after party apology?
- REALITY CHECK: What rules did Downing Street party break?
- PROFILE: What is Sue Gray investigating?
- TIMELINE: Alleged government lockdown gatherings
Mr Johnson admitted at Prime Minister’s Questions on Wednesday that he had joined colleagues for drinks in the Downing Street garden on 20 May 2020 for around 25 minutes, to thank them for their hard work during the pandemic, but had “believed implicitly that this was a work event”.
He apologised for his handling of the event, saying he understood people’s “rage”.
The gathering, described in the invitation as socially distanced, was attended by around 30 people, who were invited to bring their own alcohol. Food, including sausage rolls and crisps, was reportedly laid out on trestle tables.
The chancellor tweeted his support for Boris Johnson eight hours after the prime minister’s apology at Prime Minister’s Questions on Wednesday.
And unlike other senior ministers, Rishi Sunak was not at Boris Johnson’s side in the Commons.
Some newspapers have interpreted the timing and content of his message of support as lukewarm backing for his boss and neighbour in Downing Street.
Sources close to the chancellor point out the language he used about waiting for the report into lockdown-busting parties in Whitehall is almost identical to the messages posted by other cabinet ministers.
A peek at his diary also reveals a man with a genuinely busy day, which included a trip to Devon in the morning and a meeting with the prime minister in the evening, then more meetings with MPs worried about energy bills.
But Mr Sunak is seen as one of the favourites to succeed Mr Johnson, if and when he goes, even though the chancellor himself has said he is not interested in the top job.
The chancellor’s colleagues may be frustrated with the media’s obsession with this, but they’ll just have to live with the fact that a leadership contender always attracts more rune-reading than a lower-profile cabinet minister.
And supporters of the prime minister have started gently putting the pressure on the chancellor to speak out on other big issues facing the country.
“Problems with the cost of living? I’d have thought that was one for your finance minister, wouldn’t you?” said one adviser to a Johnson ally.
Labour, the Liberal Democrats and the SNP have called on the prime minister to resign, claiming he broke Covid rules.
Shadow health secretary Wes Streeting told the Commons: “The prime minister’s not fit to lick the boots of NHS staff in this country.”
And Labour deputy leader Angela Rayner has written to all members of the cabinet, asking whether they attended any gatherings during lockdown.
Mr Johnson’s statement and apology received a mixed reaction among Conservatives.
William Wragg, a backbench MP who chairs an influential select committee, called the prime minister’s position “untenable”.
Fellow Tory Caroline Nokes, who chairs another Commons committee, said Mr Johnson should resign, as he was “damaging the entire Conservative brand”.
The former minister, who has previously been critical of Mr Johnson’s leadership, told ITV’s Robert Peston: “Regretfully, he looks like a liability. And I think he either goes now, or he goes in three years’ time at a general election.”
But Lia Nici, Tory MP for Great Grimsby, accused the Civil Service of trying to “stitch up” the prime minister over the Downing Street drinks.
She told BBC Radio Humberside that Mr Johnson’s principal private secretary, Martin Reynolds – in whose name the invitations were sent out – should be investigated.