Britain's Labour party on Friday threatened a bid to force Prime Minister Boris Johnson out of Downing Street immediately, following his resignation in the face of a cabinet uprising.
Johnson quit as leader of the ruling Conservative party on Thursday, after a frenzy of nearly 60 resignations in less than 48 hours in opposition to his scandal-hit reign.
But the 58-year-old, whose three-year premiership has been defined by Britain's departure from the European Union and Covid, said he would stay on until his successor is found.
As candidates readied for a battle to replace him, calls mounted for Johnson to leave straight away and for an acting leader to be appointed in the interim.
Labour's deputy leader Angela Rayner said the main opposition party aimed to trigger a vote of no confidence in parliament if the Tories do not get rid of Johnson immediately.
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"He's a proven liar who's engulfed in sleaze and we can't have another couple of months of this," she told BBC radio.
"If they don't, we will call a no-confidence vote because it's pretty clear he hasn't got the confidence of the House (of Commons) or the British public."
To do so, Labour would need the support of dozens of Conservative MPs. But the strategy is fraught as it could trigger a general election, and the danger of Tory MPs losing their seats, if Johnson is defeated.
Johnson's spokesman said there was no question of deputy prime minister Dominic Raab taking over as caretaker.
"The prime minister is acting in line with convention. He remains prime minister until a new party leader is in place and the work of the government will continue whilst that takes place," he told reporters.
A timetable for the leadership contest is expected on Monday, with the winner installed in time for the party's annual conference in early October.
Defence minister Ben Wallace and Rishi Sunak -- whose resignation as finance minister on Tuesday set off the chain of exits -- were among the early frontrunners, a YouGov poll of Tories suggested.
So far, Conservative MP Tom Tugendhat and Attorney General Suella Braverman have both officially announced their candidatures, while Brexiteer Steve Baker has signalled interest.
Former health and foreign secretary Jeremy Hunt, who lost to Johnson in 2019, was "virtually certain" to run again, a source close to Hunt told British media.
In a defiant resignation speech in Downing Street on Thursday, Johnson said he was "sad... to be giving up the best job in the world".
But he said he initially refused to surrender to his "herd" of Tory critics by claiming a personal mandate he won by a landslide in December 2019.
Even while eyeing the exit, Johnson sought to steady the ship, making several appointments to replace departed cabinet members.
At a first meeting of his hastily convened new top team, Johnson confirmed his lame-duck status by saying "major fiscal decisions should be left for the next prime minister", Downing Street said.
Sunak and health secretary Sajid Javid prompted the exodus by quitting late Tuesday, just as Johnson apologised for appointing a senior colleague facing sexual assault claims to a prominent role.
Chris Pincher resigned as deputy chief whip last week following accusations he had drunkenly groped two men.
Downing Street officials eventually conceded that Johnson had known about other allegations against Pincher back in 2019, and many ministers recoiled at having to defend the PM yet again.
As late as Wednesday night, Johnson -- whose landslide 2019 win was the biggest Tory victory since the heyday of Margaret Thatcher in the 1980s -- had been defiantly clinging to power.
But he was forced to concede his time was up after another round of resignations on Thursday morning and warnings of a second no-confidence vote next week by Tory MPs.
The Tory infighting erupted as millions of Britons battle the worst slump in living standards since the 1950s, fuelled by rocketing energy prices on the back of the war in Ukraine.
Johnson's popularity had slumped since revelations about lockdown-breaking parties in Downing Street that saw him become the first prime minister to be fined in office.
Labour leader Keir Starmer and Rayner were themselves under investigation by police in northeast England over a gathering during lockdown, and had both vowed to resign if fined.
Durham police said Friday they were issuing no fines against Starmer, Rayner or 15 others at the April 2021 meeting, ruling it was a work event, not a party.