Boris Johnson’s former communications chief apologised “unreservedly” on Friday for a lockdown-breaching party in Downing Street on the eve of Prince Philip’s funeral last year — the latest in a string of allegedly rule-flouting gatherings that are threatening to topple the British prime minister.

Former Downing Street Director of Communications James Slack said his April 2021 job-leaving party “should not have happened at the time that it did.”

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“I wish to apologize unreservedly for the anger and hurt caused,” Slack said in a statement.

“I am deeply sorry, and take full responsibility,” added Slack, who left the government last year and is now deputy editor-in-chief of tabloid newspaper The Sun.

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Johnson isn’t alleged to have attended the leaving party, disclosed by the Daily Telegraph newspaper. Earlier this week, he apologized for going to an earlier gathering in the garden of Downing Street, his office and home, in May 2020, when the U.K. was under strict lockdown.

The latest party has appalled many in Britain because of the symbolism of its timing — April 16, 2021, the night before the funeral of Queen Elizabeth II’s husband of seven decades.

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The Daily Telegraph said Downing Street staff drank, danced and socialized at leaving parties for Slack and another staff member late into the night. The next day, the widowed queen sat alone in the church during her husband’s funeral service at Windsor Castle in order to adhere to social distancing rules that barred indoor mixing.

Photos of the monarch, clad in black and wearing a face mask, became a powerful image of the isolation and sacrifice endured by many during the pandemic.

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Members of Johnson’s Conservative government have expressed support for the prime minister following his admission on Wednesday that he attended a “bring your own booze” staff party in the garden of his Downing Street office in May 2020.

At the time people in Britain were banned by law from meeting more than one person outside their households as part of measures to curb the spread of the coronavirus. Millions were cut off from family and friends, and even barred from visiting dying relatives in hospitals.

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Many Conservatives fear the “partygate” scandal could become a tipping point for a leader who has weathered a series of other storms over his expenses, and his moral judgment.

The latest revelations are likely to prompt more Conservatives to join opponents and demand that Johnson resign for flouting the rules the government imposed on the country as the coronavirus swept the U.K.

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In a sign of growing anger in party ranks, the Conservative association in the staunchly Tory district of Sutton Coldfield in central England voted unanimously on Thursday night to withdraw its support from Johnson.

“The culture starts at the top, doesn’t it?” said Simon Ward, a Conservative local councillor. “And that’s the really disappointing point.

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“We were asking people all over our country to make massive sacrifices, people in rural Sutton Coldfield to make massive sacrifices, over the last two years. I think we have the right to expect everybody in government and in those positions of leadership to follow those same rules and guidelines as well.”

Johnson said in his apology on Wednesday that he understood public “rage,” but stopped short of admitting wrongdoing, saying he had considered the gathering a work event to thank staff for their efforts during the pandemic.

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Johnson urged people to await the conclusions of an investigation by senior civil servant Sue Gray into multiple alleged rule-breaking parties by government staff during the pandemic. Gray, a respected public servant who has investigated past allegations of ministerial wrongdoing, is expected to report by the end of the month.

The government says Gray’s inquiry is independent, but she is a civil servant and Johnson is, ultimately, her boss. Gray could conclude that Johnson broke the code of conduct for government ministers, though she does not have the power to fire him. Johnson has not said what he will do if she found he was at fault.

Johnson does not have to face voters’ judgment until the next general election, scheduled for 2024. But his party could seek to oust him sooner if it judges he has become toxic.

Under Conservative rules, a no-confidence vote in the leader can be triggered if 15% of party lawmakers write letters demanding it.

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Roger Gale, a Conservative lawmaker who has long been critical of Johnson, said he had already submitted a letter calling for a leadership challenge.

“I do think that minds are now, over this weekend, being focused upon the need to take the necessary action,” he said. “I clearly don’t know, and I shouldn’t know, how many of my colleagues have put in letters … but I believe that there is some momentum which is growing.”

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Foreign Secretary Liz Truss — often cited as a potential successor to Johnson — said she understood “people’s anger and dismay” at the party revelations.

But she said “I think we now need to move on.”