LONDON — Prime Minister Boris Johnson is set to become the first British leader in recent history to be investigated for lying to Parliament, after lawmakers on Thursday gave a nod to an inquiry on whether he intentionally misled them about government parties at Downing Street that broke pandemic lockdown rules.

This would be the third investigation into what’s become known as Partygate. A criminal investigation by London’s Metropolitan Police and a probe by senior civil servant Sue Gray are both pending. Both have already identified wrongdoing. Last week, Johnson became the first serving prime minister found to have broken the law, and more citations could be coming.

But his political future may rest less on the determination of how many times he and his staff violated their own rules and more on whether lawmakers are upset about how he presented the situation to them. If Parliament’s privileges committee finds him in contempt – that he knowingly misled lawmakers – he could be suspended from Westminster, expelled or pressured to resign.

Britain’s Prime Minister Boris Johnson waves to the media as he leaves 10 Downing Street for the House of Commons to make a statement about Downing Street parties during the coronavirus lockdowns, in London on Tuesday. Alastair Grant/Associated Press

As revelations about lockdown parties were coming to light, Johnson told Parliament in December: “The guidance was followed and the rules were followed at all times.” On another occasion that month, he said: “I have been repeatedly assured since these allegations emerged that there was no party and that no COVID rules were broken.”

After police determined last week that, yes, in fact, rules were broken – by Johnson, his wife, Chancellor Rishi Sunak and others – Johnson apologized and paid a $65 fine. But he maintained he had not lied.

In a statement to Parliament on Tuesday, Johnson said: “Not by way of mitigation or excuse but purely because it explains my previous words in this House – 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.”

His citation was for attending a gathering on his birthday on June 19, 2020, that he says lasted less than 10 minutes. Police are investigating a dozen government gatherings – including a “bring your own booze” garden party, Christmas parties and goodbye parties – that took place while the government was imposing tight restrictions on how many people from different households could meet.

It was the opposition Labour Party that called for the contempt probe.

“Telling the truth matters in our politics,” Labour leader Keir Starmer said during Thursday’s debate.

“They say, ‘there are worse crimes, he didn’t rob a bank, he only broke the rules for 10 minutes, it was all a long time ago.’ Every time one of these arguments is trotted out, the status of this house is gradually eroded and our democracy becomes a little weaker,” Starmer said.

“The convention that Parliament must not be misled, and that in return, we don’t accuse each other of lying, are not curious quirks of this strange place, they are fundamental pillars on which our constitution is built,” he said.

Because Johnson’s Conservative Party has an 80-seat majority, it usually has no trouble squashing the opposition party’s motions. But in this case, enough Conservative lawmakers are uncomfortable with what Johnson has done – or at least don’t want to be seen as blocking an investigation. British commentators said it was a sign that the prime minister had lost control of his party.

The motion was “nodded” through without a formal vote, meaning no names were recorded that would reveal dissent within the Tory ranks. But several Conservative lawmakers rose during the marathon debate to express their frustration with Johnson.

Steve Baker, a senior Conservative, was among those who called on Johnson to stand down. “For not obeying the letter and the spirit … the prime minister now should be long gone,” he said.

William Wragg, another Conservative, dismissed suggestions that the prime minister should stay in his post because of the war in Ukraine. “The invasion of a sovereign nation by a dictatorial aggressor should not be a reason why we should accept lower standards ourselves,” he said.

Johnson on Thursday was 4,000 miles away, in India for trade talks. He took time out of his schedule to tweet birthday wishes to Queen Elizabeth II. He told reporters traveling with him that he wanted to “get on with the job.”

Asked to respond to calls for him to quit, he said, “I understand people’s feelings. I don’t think that is the right thing to do.”

In Britain, misleading Parliament – or breaking the “ministerial code” politicians are supposed to follow – is normally a resigning offense. But that is a convention, rather than an iron-clad rule. And the enforcer of the ministerial code is the British leader – a detail that Green Party lawmaker Caroline Lucas on Thursday called “beyond ludicrous.”

While many Conservatives are increasingly unhappy with their leader, there’s no indication that they are about to jettison him. About 16 Conservative lawmakers have publicly said that Johnson shouldn’t lead the party into the next election – far less than the 54 needed to trigger a leadership challenge.

Parliament won’t begin its contempt investigation until the Metropolitan Police finish their investigation, lawmakers said Thursday. And the police said Thursday they wouldn’t issue any more fines until after local elections on May 5.

So the cloud will linger over Johnson for some time still.