LONDON >> British Prime Minister Boris Johnson today offered what he said was a “wholehearted” apology for attending an illegal party during lockdown — but insisted he didn’t knowingly break rules or mislead Parliament, and brushed off calls to resign.

Johnson told lawmakers in the House of Commons that it simply “did not occur to me” that the birthday gathering, complete with a cake, was a party.

That excuse was greeted with derision by opposition politicians — and some among the governing Conservatives — who have called with increasing frustration for Johnson to quit since stories began to circulate late last year of parties in the prime minister’s office and other government buildings in 2020 and 2021, when millions in the country were barred from meeting with friends and family or even attending funerals for their loved ones.

Opposition Labour Party leader Keir Starmer branded the apology “half-hearted” and “a joke.”

Last week, Johnson was fined $66 for attending his own surprise birthday party in 10 Downing St. in June 2020, making him the first British prime minister ever found to have broken the law while in office.

Speaking as the House of Commons returned from an 11-day Easter break, Johnson acknowledged people’s “hurt and anger,” but added that “it did not occur to me then or subsequently that a gathering in the Cabinet Room, just before a vital meeting on COVID strategy, could amount to a breach of the rules.”

Starmer said that excuse would ring hollow with ordinary people who “understand that the rules apply to all of us,” and he challenged Conservatives to “bring an end to this shameful chapter” and jettison Johnson.

“He knows he’s dishonest and incapable of changing,” Starmer said. “So he drags everybody else down with him.”

Starmer was told off by House of Commons Speaker Lindsay Hoyle for accusing another member of dishonesty — a breach of parliamentary rules. Minutes later, Labour lawmaker Karl Turner also was chastised by the Speaker after branding Johnson a liar.

“I withdraw the word ‘liar,’ Mr. Speaker,” Turner said. “But the electorate will already have decided.”

Labour has not given up on trying to get lawmakers to censure Johnson over the “partygate” scandal. Speaker Hoyle said he would allow Labour to hold a Commons debate and vote Thursday on whether Johnson should be investigated for allegedly misleading Parliament. Ministers found to have done that knowingly are generally expected to resign.

Johnson is due to be out of the country Thursday on a visit to India, and the big Conservative majority in Parliament means the measure is unlikely to pass. But the vote will force Tory lawmakers uneasy with the prime minister to publicly back him or criticize him.

Johnson insisted today that he was contrite, but argued it would be wrong to change leaders while Britain faces crises including the war in Ukraine and a cost-of-living squeeze driven by surging energy and goods prices.

Johnson’s grip on power had appeared to be on a knife-edge earlier this year amid police and civil service investigations into the parties, and the departure of several top aides.

Allies feared “partygate” could become a tipping point for a divisive but resilient leader who has weathered a series of other storms over his expenses and his moral judgment. Some Conservative lawmakers were openly calling for a no-confidence vote in Johnson.

But Johnson has hung on, partly because Russia’s invasion of Ukraine has seized public and political attention.

Johnson’s international image, battered by Britain’s messy exit from the European Union under his leadership, has been revived by his firm military, political and moral support for Ukraine. Johnson traveled to Kyiv earlier this month to meet with President Volodymyr Zelenskyy.

Johnson’s troubles are not over and he could still face more fines. London’s Metropolitan Police force is investigating a dozen events, including “bring your own booze” office parties and “wine time Fridays,” and Johnson is reported to have attended several of them. So far at least 50 tickets have been handed out, including those to Johnson, his wife Carrie and Treasury chief Rishi Sunak.

If Johnson is sanctioned again, calls for a no-confidence vote could grow among Conservatives. For now, many are biding their time, and looking to see whether public anger translates into losses for the party at local elections across the country on May 5.

Conservative lawmaker Geoffrey Clifton-Brown said his colleagues were “withholding their judgment and waiting to see what happens.”

But fellow Conservative Mark Harper, a former government chief whip, said Johnson “broke the laws that he told the country they had to follow” and “hasn’t been straightforward about it.”

“I’m very sorry to have to say this, but I no longer think he is worthy of the great office that he holds,” Harper said.