LONDON — Facing a potentially lethal threat to his leadership, Prime Minister Boris Johnson of Britain on Wednesday offered a contrite apology in Parliament for attending a garden party at 10 Downing Street while the country was under lockdown. He acknowledged that he had deeply offended the public, even as he claimed that he had not breached his government’s regulations on gatherings during the early days of the pandemic.
“I want to apologize,” Mr. Johnson said during an extraordinarily tense session of Prime Minister’s Questions. “I know there are things we simply did not get right, and I must simply take responsibility.”
The prime minister said that he viewed the party, on May 20, 2020, as “implicitly a work event,” an opportunity to thank Downing Street staff members for their efforts during the initial phase of the coronavirus pandemic. But he said he understood that the British public, who were being told not to meet more than a single person outside their households, would view it as a double standard.
“With hindsight, I should have sent everybody back inside,” Mr. Johnson said. “I should have found some other way to thank them.”
The prime minister’s apology did not mollify the leader of the opposition Labour Party, Keir Starmer, who dismissed Mr. Johnson’s display of contrition, accused him of serial duplicity and demanded that he step down.
“The party is over, prime minister,” Mr. Starmer said, asking, “Is he now going to do the decent thing and resign?”
Mr. Johnson rejected that, asking for Parliament to wait for the findings of an internal investigation by a senior civil servant, Sue Gray. But he looked beleaguered under a torrent of hostile questions from Mr. Starmer, a former public prosecutor, offering little in the way of a defense and repeatedly apologizing for having mishandled the situation.
Pressure has been mounting steadily on Mr. Johnson since the emailed party invitation emerged late Monday with clear signs that his support within the Conservative Party was waning. On Tuesday, when Mr. Johnson sent out a ministerial colleague to defend him in Parliament, few of his own lawmakers turned out in support.
For Mr. Johnson, one of the greatest risks is the evidence that he misled Parliament in his previous statements — the kind of transgression that once might have forced a prime minister to resign. On Dec. 8, he declared in the House of Commons, “I repeat that I have been repeatedly assured since these allegations emerged that there was no party and that no Covid rules were broken.”
A week later, Mr. Johnson told reporters, “I can tell you once again that I certainly broke no rules.” On Dec. 20, after The Guardian newspaper published a photograph of the prime minister mixing with colleagues over wine and cheese in his garden during a lockdown, he said, “Those were people at work, talking about work.”
After the most recent disclosure — of the larger party that he also attended — Mr. Johnson stopped offering any response, saying that he would wait for the findings of the internal investigation.
Unlike other ethics questions that have clouded Mr. Johnson throughout his career, the furor over parties has stuck a chord with the public. People vividly remember the grim months early in the pandemic, when they were told to isolate at home, and forbidden from visiting elderly parents, even if they became ill.