Ori deputies will choose who they want to be their new leader in the first leg of the race for 10th place Boris Johnson abruptly dropped out of the competition.

The former prime minister claimed he had the nominations needed to get on the ballot, but admitted he could not unite his warring party.

His withdrawal means the contest could be decided on Monday afternoon if both remaining candidates fail to win the support of 100 MPs.

In a statement on Sunday night, Mr Johnson said there was a “very strong possibility” he could be back in No 10 by the end of the week if he stood.

However, his efforts to “reach out” to competitors – Rishi Sunak and Penny Mordant – joint work in the national interests was not successful, so he dropped out of school.

While Sunak, the former chancellor, already has more than 140 public declarations of support, Ms Mordaunt, the leader of the House, has had fewer than 30.

Her team now hopes that Mr Johnson’s departure will see a streak of MPs who have supported him or who have not yet announced their defection.

A campaign source confirmed she is still in the running, claiming she is the candidate Labor fears most.

A penny is the unifying candidate most likely to keep the wings of the Conservative Party together, and polls show she is the most likely candidate to retain the seats won by the Conservative Party in 2019,” the source said.

However, one senior minister who supported Mr Johnson – Chancellor of the Duchy of Lancaster Nadhim Zahavi – said he would now back Mr Sunak.

“Rishi is very talented and will command a majority in the Parliamentary Conservative Party and will have my full support and loyalty,” he tweeted.

With nominations closing at 2pm on Monday, Ms Mordaunt has limited time to get the nominations she needs. If unsuccessful, Mr. Sunak will be declared the uncontested leader.

If she does get the numbers, MPs will decide which of the two candidates they prefer in an “indicative” vote.

A final online poll of party members will then be held to determine the result, which will be tallied on Friday – unless one of the candidates withdraws.

There are certainly some in the party who would like to see an uncontested “coronation” to avoid a repeat of what happened to Liz Truss, when the party nationally voted in a leader who did not have the support of MPs.

Ms Mordaunt could come under pressure to withdraw if she trails Mr Sunak in MP polls, despite being popular with the Tories.

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 vote in the contest.

In a statement on Sunday night, Mr Johnson said he was “surprised” by the support he had received from people calling for him to run just weeks after his own MPs were forced out of office after too many scandals.

Had he run, he said there was a “very good chance” his friends would have returned him to Number 10 by the end of the week and that he would be “well placed” to lead the party to victory in the 2024 general election.

However, he concluded that “it just wouldn’t be right.”

“You cannot govern effectively if you don’t have a single party in parliament,” he said.

“And although I reached out to Risha and Penny – because I hoped we could come together in the national interest – we unfortunately couldn’t work out a way to do that.

“I believe I have something to offer, but I’m afraid it’s just not the right time.”

Some MPs were skeptical of his claim that there were 100 nominations needed to move forward, with public declarations of support well below that number.

Some in Westminster suspected he chose to quit rather than face the humiliation of admitting he couldn’t get the numbers.