Boris Johnson has pulled out of the race for Prime Minister admitting he cannot unite the Conservative Party.

The former prime minister said he had “reached out” to rivals Rishi Sunak and Penny Mordaunt to see if they could work together in the national interest. However, he said this had not proved possible.

In a statement, he claimed he had secured the 100 nominations needed to get onto the ballot paper and that if he stood there was a “very good chance” he would be back in Downing Street by the end of the week.

He went on: “But in the course of the last days I have sadly 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.

“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.

“Therefore I am afraid the best thing is that I do not allow my nomination to go forward and commit my support to whoever succeeds.”

Johnson’s withdrawal from the race leaves the election to replace Liz Truss as potentially a straight fight between Sunak, the former chancellor, and Mordaunt, the Leader of the House.

The new prime minister could be announced after 2pm on Monday if Mordaunt fails to receive enough nominations to go forward.

A source from the Mordaunt campaign confirmed that she remained in the race.

“Penny is the unifying candidate who is most likely to keep the wings of the Conservative Party together and polling shows that she is the most likely candidate to hold onto the seats the Conservative Party gained in 2019,” the source said.