Penny Mordaunt has dropped out of the Conservative leadership race at the last minute, paving the way for Rishi Sunak to become the next prime minister.

The leader of the Commons had struggled to get fellow MPs to publicly declare their support as the number of those backing former chancellor Mr Sunak surged.

Party rules meant each candidate needed at least 100 nominations by Monday afternoon to stay in the race.

Ms Mordaunt only had 25 public backers as of Monday morning, though a source from her campaign team claimed she had up to 90 nominations and would not be pulling out of the race.

Ms Mordaunt conceded minutes before the results were due to be announced, writing in a tweet: “These are unprecedented times. Despite the compressed timetable for the leadership contest it is clear that colleagues feel we need certainty.

“They have taken this decision in good faith for the sake of the country.”

She added: “We all owe it to the country to each other and to Rishi to unite and work together for the good of the nation.

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Her decision came after Boris Johnson also withdrew from the contest on Sunday evening, despite claiming he had the backing of at least the 100 MPs required to make it on to the ballot.

The former prime minister said he had “cleared the very high hurdle of 102 nominations”, but came to the conclusion that “this is simply not the right time” for his return to frontline politics – just six weeks after he was officially ousted.

It is not clear how many nominations Ms Mordaunt received.

Bob Seely, who was a key backer of Ms Mordaunt, told Sky’s political editor Beth Rigby: “We were pretty close, it was touch and go. I don’t know the numbers, but I know we were close.”

He added: “What is critical now is that we give Rishi 100% of our support – we have to remember that our opponents are in front of us in the House of Commons, not behind us. We have got to come together.”

His comments were echoed by James Cleverly, the foreign secretary and one of several cabinet ministers to back Mr Sunak following Mr Johnson’s withdrawal.

Announcing the results of the leadership race, Sir Graham Brady, chairman of the powerful 1922 committee, said the Conservative Party only received one “valid” nomination to be the leader and therefore prime minister – Mr Sunak.

Had Ms Mordaunt stayed in the race and received over 100 nominations, the vote would have gone to party members.

The MP for Portsmouth North, who came third in the race to become prime minister last time round, was the first candidate to declare her leadership bid on Friday afternoon.

The second leadership contest in three months began last Thursday after the extraordinary resignation of Liz Truss.