U.K. Prime Minister Boris Johnson was fighting for his political future Friday as outrage mounted after his belated apology for attending a party during lockdown and as a fresh report emerged of other raucous gatherings at his office.

Revelations that Johnson and Downing Street staff breached restrictions at the height of Britain's coronavirus lockdown have enraged the public, who were forced to abide by rules that prevented them from visiting sick and dying loved ones or attending funerals.

The scandal looked set to deepen Friday as the conservative-leaning Daily Telegraph published an exclusive claiming Johnson's staff held an alcohol-fueled party just hours before the socially distanced funeral of Prince Philip in April 2021.

The image of Queen Elizabeth sitting alone in church at her late husband's memorial service was one of the starkest images of Britain under lockdown.

Most Cabinet members have rallied around Johnson after his mea culpa, but the backing from potential successors such as powerful Finance Minister Rishi Sunak has been distinctly lukewarm.

While expressing "heartfelt apologies," Johnson sparked ridicule this week by saying he had believed a May 2020 gathering in the Downing Street garden – at which more than 100 people gathered – was a work event. He urged all sides to await the findings of an internal inquiry.

Douglas Ross, the Conservatives leader in Scotland, has joined at least four Tory backbench members of Parliament (MPs) in calling for Johnson to quit after the prime minister admitted joining the party.

"Regretfully, I have to say his position is no longer tenable," Ross told STV.

Cabinet member Jacob Rees-Mogg dismissed Ross as a "lightweight" Tory figure, sparking rebukes from other MPs and warnings that the upper-crust Englishman was bolstering the case for Scottish independence.

Northern Ireland Secretary Brandon Lewis has insisted Johnson had been "very, very sincere" in his apology, amid warnings that Conservative MPs could be mobilizing for a no-confidence vote.

But Lewis was forced to play down reports that Johnson had in the wake of his House of Commons apology told Ross and other Tories that he did not believe he had done anything wrong.

On Wednesday, Labour leader Keir Starmer for the first time joined other opposition chiefs in demanding Johnson's resignation.

The prime minister's poll ratings have slumped since "partygate" allegations emerged last month.

One new poll by YouGov in The Times newspaper gave Labour a 10-point lead over the Tories, its biggest margin since 2013, and said six out of 10 voters believe Johnson should resign.

London's Metropolitan Police have not ruled out a criminal probe into the May 2020 party, which occurred at a time when Britons were banned from outdoor socializing.

But for now, Johnson's fate appears to lie in the hands of senior civil servant Sue Gray, whom he has commissioned to look into the May 2020 event and other Downing Street gatherings that year.

Chancellor of the Exchequer Sunak, who was noticeably absent from the House of Commons on Wednesday, said Johnson had been right to apologize and urged "patience" pending Gray's report.

Another potential contender to replace Johnson, Foreign Secretary Liz Truss, also took hours to issue any public backing, but later said she stood "100 percent" behind the prime minister.

Johnson's official spokesperson insisted the Cabinet was united in delivering the government's post-Brexit and post-pandemic priorities.

"The prime minister abides by the principles of public office," he told reporters, stressing that Johnson had promised to publish Gray's report and then update Parliament.