Boris Johnson is set to apologise for breaking his own lockdown laws when he makes his first statement to MPs since being fined by police.
The prime minister is expected to say he did not knowingly break the rules at a 2020 birthday party at No 10.
Opposition parties have accused him of lying to Parliament after he previously told them no rules had been broken.
Mr Johnson has vowed to "set the record straight" when he speaks to MPs at about 3.30pm.
But he is also expected to urge MPs to focus instead on issues such as rising prices and the war in Ukraine.
Speaking to ITV, Labour leader Sir Keir Starmer accused the PM of using the conflict in Ukraine as a "shield" to keep his job, adding that he finds such a tactic "pretty offensive".
Sir Keir predicted: "He will try an try an apology, and he will immediately then go into excuses".
Labour and the other opposition parties are exploring ways to hold the prime minister to account, such as a censure motion, effectively a slap on the wrist, or a vote of no confidence.
But shadow attorney general Emily Thornberry said a coup by Tory MPs was needed to remove the prime minister.
She told BBC Radio 4's Today programme: "Whatever means we take, the difficulty we will always have is that, since the 2019 election, the Conservatives have an 80-seat majority when there is a vote.
"Unless Conservative MPs can look at their consciences and vote the right way, we are not going to get the sort of result that we should get."
Commons Speaker Sir Lindsay Hoyle is expected to decide around lunchtime what vote - if any - should take place on measures against the prime minister.
Mr Johnson became the first serving UK prime minister to be sanctioned for breaking the law when, along with his wife Carrie and Chancellor Rishi Sunak, he was fined last week for attending the birthday event held for him in the Cabinet Room in June 2020.
The PM is facing accusations of lying to MPs because he initially told them Covid rules had been followed in No 10 after the first reports of parties emerged last year.
Under government rules, ministers are expected to resign for knowingly misleading MPs - and correct the record as soon as possible if they inadvertently tell Parliament something false.
Mr Johnson has since said it "did not occur" to him at the time of the gathering that it could be in contravention of Covid lockdown rules.
On Monday, Transport Secretary Grant Shapps said what happened was "wrong", but argued Mr Johnson had not "knowingly" misled MPs.
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