LONDON (AP) -- British Prime Minister Boris Johnson faces a grilling from opponents in Parliament on Wednesday - and a more worrying threat from his own party's restive lawmakers, dozens of whom are plotting to oust him over a string of lockdown-flouting government parties.

Conservative legislators are judging whether to trigger a no-confidence vote in Johnson amid public anger over the “partygate” scandal. It's a stunning reversal of fortune for a politician who just over two years ago led the Conservatives to their biggest election victory in almost 40 years.

Johnson and loyal ministers were using a mix of pressure and promises in an effort to bring rebels back into line before they submit letters to a party committee calling for a vote of no confidence.

Under Conservative Party rules, a no-confidence vote in the party's leader can be triggered if 54 party lawmakers write letters to a party official demanding it.

So far only a handful of Conservative members of Parliament have openly called for Johnson to quit, though several dozen are believed to have submitted letters, including some legislators elected as part of a Johnson-led landslide in December 2019.

Conservative lawmaker Andrew Bridgen, who is calling for a change of leader, said he thought the 54-letter threshold would be reached “this week,” setting the stage for a confidence vote within days.

If Johnson lost a confidence vote among the party's 360 lawmakers, it would trigger a contest to replace him as Conservative leader. The winner would also become prime minister.

The weekly Prime Minister's Questions session in the House of Commons on Wednesday comes a week after Johnson apologized to lawmakers for attending a “bring your own booze” gathering in garden of his Downing Street offices in May 2020. At the time, people in Britain were barred from meeting more than one person outside their household to help curb the spread of the coronavirus.

Johnson said he had considered the party a work gathering that fell within the rules.

“I'm absolutely categorical, nobody said to me, `This is an event that is against the rules,”' Johnson said Tuesday.

Senior civil servant Sue Gray is investigating claims that government staff held late-night soirees, boozy parties and “wine time Fridays” while Britain was under coronavirus restrictions in 2020 and 2021. The allegations have spawned public anger, incredulity and mockery as well as prompted a growing number of Conservatives to call for Johnson's resignation.

Gray's report is expected to be published by the end of the month.

Johnson's apologies - in which he acknowledged “misjudgments” but did not personal rule-breaking - appear to have weakened, rather than strengthened, his position in the party.

He has urged his opponents to wait for Gray's verdict, though experts say there is a good chance the investigation will neither exonerate him nor conclude the prime minister broke the law.

Even lawmakers who have backed Johnson say he would have to resign if he is found to have lied.

Armed Forces Minister James Heappey said members of the public were “absolutely furious.”

“I am angry, too,” Heappey told Times Radio, but added that “the prime minister has stood up at the despatch box and set out his version of events and apologized profusely to the British public.”

“I choose to believe what the prime minister has said. But I know that that's not good enough for many of my constituent,” he said.