Penny Mordaunt was desperately battling for support from Tory MPs to prevent Rishi Sunak being installed as prime minister without a vote of the party membership after Boris Johnson scrapped his comeback bid.
Mr Sunak, a former chancellor, is the firm frontrunner as he commands the public support of around half the parliamentary party – far more than the 100 nominations needed by the 2pm deadline.
With a little over two hours to spare, Ms Mordaunt’s campaign claimed to have received the support of at least 90 Conservative MPs and urged others to back her so party members can have their say in an online ballot.
The Commons Leader would face Mr Sunak in an online ballot if she reaches the threshold on Monday, but if she fails then her rival will succeed Liz Truss as the Tory leader in a “coronation”.
A Government source said Mr Sunak, who lost to Ms Truss in the last contest just seven weeks ago, could become prime minister later in the day if he becomes the only candidate, though Tuesday is seen as more likely.
Ms Mordaunt’s campaign allies insisted they were “confident” she would reach the threshold and claimed she had a far higher tally than the around 26 declarations of support that have been made public.
A campaign source said: “We have now passed 90. For the sake of the party, it’s important our members have their say.”
The pound, after a torrid time under Ms Truss, continued to rise and the gilt market cooled, making it cheaper for the Government to borrow money, as Mr Sunak edged towards No 10.
Mr Johnson had returned home from a Caribbean holiday as he plotted a return to No 10 less than two months after being ousted following a series of scandals, but later ruled out standing.
In a statement on Sunday evening, he said there was a “very good chance” he could have been back in No 10 by the end of the week if he had stood but admitted he could not unite his warring party.
Mr Johnson’s efforts to “reach out” to his rivals – Mr Sunak and Ms Mordaunt – to work together in the national interest had not been successful, he said, so he was dropping out.
He lagged far behind Mr Sunak in public declarations of support but claimed to have amassed at least 102 nominations.
Mr Sunak has received backing from about half of the 357 Tory MPs, giving him grounds to say he is the best-placed candidate to try to govern the unruly party.
Ms Mordaunt, who has around 26 public supporters, will be trying to convince Johnson backers to come over to her side but Mr Sunak appeared to be the immediate beneficiary.
Foreign Secretary James Cleverly called for colleagues to back Mr Sunak as the candidate with the “most experience” and former Cabinet minister Michael Gove said the Tories must “unite behind” Mr Sunak.
But Mordaunt-backer Damian Green told BBC Radio 4’s Today programme: “We’re confident of getting to 100 before the deadline of 2pm and putting the case to colleagues that Penny is the person best positioned to unify the party, she’s got support from all wings of the party already and we can then get on with the important job for the country of the various serious problems we’re facing.”
Victory for either Mr Sunak or Ms Mordaunt will mean the Tories are on to their third prime minister since they won the 2019 general election under Mr Johnson’s leadership.
Veteran Tory Sir Christopher Chope joined Labour in demanding a fresh general election, arguing it is the only solution for the next leader now the Conservative Party is “ungovernable”.
The MP for Christchurch in Dorset, which he held last time with a near-25,000 vote majority, told Today: “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, and so I must say I’m very pessimistic, I’m very angry, and I feel that Boris has been let down once again and undermined by our parliamentary colleagues.”
If Ms Mordaunt does win enough support to make the next stage, MPs will decide which of the two candidates they prefer in an “indicative” vote.
There will then be a final online poll of party members to decide the outcome, with the result due on Friday – unless one of the candidates pulls out.
Ms Mordaunt could find herself under pressure to withdraw if she finishes a long way behind Mr Sunak in the poll of MPs, should it go to a vote, even though she is popular with the Tory grassroots.
At the same time, however, many activists – many of whom loathe Mr Sunak for his role in bringing down Mr Johnson – will be furious if they are denied a say in the contest.
In a statement on Sunday evening, Mr Johnson said he had been “overwhelmed” by the support he had received from people urging him to run just weeks after being forced out by his own MPs after one scandal too many.
If he had stood, he said there was a “very good chance” the members would have voted him back into No 10 by the end of the week and that he would have been “well-placed” to lead the party to victory in a general election in 2024.
However, he said he had come to the conclusion that “this would simply not be the right thing to do”.
“You can’t govern effectively unless you have a united party in Parliament,” he said.
“And though I have reached out to both Rishi and Penny – because I hoped that we could come together in the national interest – we have sadly not been able to work out a way of doing this.
“I believe I have much to offer but I am afraid that this is simply not the right time.”
There were MPs expressing scepticism at his claims to have secured the 100 nominations needed to go forward, with the number of public declarations of support falling far short of that.
Some at Westminster suspected that he chose to withdraw rather than face the humiliation of having to admit he could not get the numbers.