MPs will hold a vote of no confidence in the Tory government after it emerged Boris Johnson will cling to office until September 5.
Labour is due to table a formal no-confidence motion in the government on Tuesday - the first of its kind for three and a half years.
A debate and vote is likely in the House of Commons on Wednesday.
If it passes, the convention is that Mr Johnson’s government would either resign or seek a general election.
But despite Tory MPs forcing him out, defeat for Mr Johnson seems highly unlikely. He has a 73-seat majority and Conservatives are unlikely to vote down their own government when they know a new leader is on the way.
Jeremy Corbyn ’s no confidence motion in Theresa May ’s government failed in 2019 and the last successful no confidence motion was in 1979, bringing down the government of James Callaghan.
Before that the last defeat was in 1924.
It comes after Keir Starmer vowed a no confidence vote in the government if Mr Johnson tried to cling to office.
A Labour source told HuffPost UK: “It will put the squeeze on backbench Tories to either vote for him, and be hypocrites, or back Labour, admitting we were right.
“Do all those Tory leadership candidates really want to be answering that question next week? They know he needs to go.”
Previously a no confidence defeat would trigger a general election automatically if no new government was found within 14 days. This is no longer the case because the law it was based on, the Fixed Term Parliaments Act, has been repealed.
Mr Johnson has denied he has plans to stand himself in the leadership race after announcing he would resign as prime minister last week.
Outside Downing Street last Thursday, Mr Johnson said: "It is clearly now the will of the parliamentary Conservative Party that there should be a new leader of that party and therefore a new prime minister.
"And I've agreed with Sir Graham Brady, the chairman of our backbench MPs, that the process of choosing that new leader should begin now and the timetable will be announced next week."
Previously a no confidence defeat would trigger a general election automatically if no new government was found within 14 days. This is no longer the case because the law it was based on, the Fixed Term Parliaments Act, has been repealed.
