Rishi Sunak is on course to be named as the next Prime Minister as early as today after Boris Johnson bottled his leadership bid.
The former Chancellor has secured the backing of more than half of all 357 Conservative MPs as declarations ticked up to 180 with only hours left until the 2pm nomination deadline.
Rival Penny Mordaunt has refused to bow out and is scrambling to hit the 100-MP threshold to get onto the ballot paper, with fewer than 30 publicly declared backers.
A source on her campaign claimed she had the support of more than 90 MPs - significantly higher than the published tally.
The source added: "For the sake of the party, it's important our members have their say."
Both candidates are battling to persuade Mr Johnson's supporters to switch allegiance after the scandal-hit former PM sensationally pulled out of the race on Sunday night.
Mr Sunak, who lost out to Liz Truss in the summer leadership contest, will be handed the keys to No10 if Ms Mordaunt fails to get onto the ballot paper. Dozens of MPs have still not declared.
The new PM will not be officially confirmed until they are invited to form a government by King Charles.
A Government source said the new PM could be in place as soon as Monday if the Tory leadership contest does not progress further.
If both candidates get 100 backers then it will go into a run-off for the membership. Whoever gets the most support will be named as Tory leader on Friday morning.
Ms Mordaunt has refused to pull out of the race, with a campaign spokesperson saying she is getting close to the numbers she needs to get on the ballot.
The spokesperson said: "Penny is speaking to colleagues from across the party. She’s getting the numbers and she’s in it to win it.
"Penny has always been a campaigner - she took her seat from Labour and she’s fought for it ever since. The party needs a fresh start to ensure it wins the next General Election and holds the seats it gained in 2019."
Digital Minister Damian Collins, one of her backers, said it was "all to play for" and claimed "a lot of people" had "instantly" switched their allegiance from Mr Johnson to Ms Mordaunt.
"I think it is all to play for today in terms of whether Penny can get the 100 votes she needs to make sure there is a members ballot," Mr Collins told Times Radio.
"I think it would be all to play for if there was a ballot of the members and some of the polling that has been released shows... there's a high degree of trust for Penny."
But Mr Sunak has picked up some high profile Johnson backers, including former Home Secretary Priti Patel, Levelling Up Secretary
Ms Patel tweeted this morning that it was time to "unite by putting public service first and work together".
She said: "We care about our country and with the enormous challenges upon us we must put political differences aside to give Rishi Sunak the best chance of succeeding."
Home Secretary Grant Shapps, who is supporting Mr Sunak, said the ex-Chancellor did not believe he had the race "in the bag", adding: "He's speaking to colleagues this morning, he's working very hard to attract those supporters who were perhaps with Boris Johnson previously."
Mr Sunak only declared his candidacy on Sunday - and has so far done no media interviews about his plans to be Prime Minister.
Mr Shapps insisted that he would stand on the basis of the 2019 manifesto - much of which was junked by Liz Truss.
He told Sky News: "We elect a party and we elect individuals as members of that party, and the 2019 manifesto is actually the thing - the document, if you like - that Rishi is standing on."
The European Research Group of right-wing Brexiteers failed to unite around a single candidate, offering a glimmer of hope to Ms Mordaunt.
ERG chairman Mark Francois said: “We believe we have one and potentially two extremely strong options to be leader of the Conservative Party.
“But as a group we were unable to collectively endorse either candidate.”
He said members had spoken to both candidates and both had promised to take a “very robust line on the Northern Ireland Protocol”.
Some Boris Johnson backers are demanding a general election as they say Mr Sunak doesn't have a mandate for the top job.
Sir Christopher Chope, Conservative MP for Christchurch, has said the party is "ungovernable" and a general election is "the only answer".
Speaking to BBC Radio 4's Today programme, he said: "If people who are now seeking the crown want to have the respect which comes from having a mandate, then what I'm saying is that the best way they can get that respect is by winning a mandate with the people, and that's why I think a general election is essentially the only answer, otherwise we're just going to go from bad to worse.
"The party is ungovernable in the House of Commons and so we're going to have continuing rebellions as we try to change policies and so on."
Staunch Johnson loyalist Nadine Dorries said an election was now "impossible to avoid".
"Boris would have won members vote - already had a mandate from the people," she tweeted.
"Rishi and Penny, despite requests from Boris refused to unite which would have made governing utterly impossible. Penny actually asked him to step aside for her. It will now be impossible to avoid a GE."
The Mirror is campaigning for a general election to end the Tory chaos, which has resulted in three Prime Ministers this year.
