Boris Johnson pulled out of the race to become Britain's next prime minister after a day in which he was accused of failing to win the support of 100 Conservative MPs.

Despite frantic attempts by Johnson to bolster his support, he announced at 9pm on Sunday that he was abandoning his bid to make a comeback as prime minister.

Rishi Sunak, a former chancellor, is the clear favourite to become Conservative leader and prime minister.

Johnson said in a statement on Sunday that he had withdrawn from the party and the national interest, but that he had the support of 100 MPs.

He said he could put his nomination in tomorrow after clearing the high hurdle of 102 nominations, including a proposer and a seconder.

A member of Sunak's camp disagreed.

Johnson was struggling to win over more than a few new supporters. Johnson had 52 MPs compared to Sunak's 130.

The leader of the House of Commons is supported by less than 30 Conservative MPs.

Sunak will become prime minister if she doesn't get 100 nominations by 2pm on Monday.

Johnson said in a statement that his withdrawal was completely altruistic, just 12 hours after he urged supporters to redouble their efforts to get him on the ballot.

He said that a general election would be a disaster because it would distract the government from the economic pressures faced by families.

Johnson claimed to have more than 100 backers when nominations closed on Monday, but his rivals think he may have been wrong. Johnson said he would have won if the contest was open to the party's members.

He said there was a good chance that he would be successful in the election with Conservative party members and that he could return to the Prime Minister's office on Friday.

I have concluded that this would not be the right thing to do. If you don't have a united party in parliament, you can't govern.

We have not been able to come together in the national interest because we have not been able to find a way to do this.

I don't want my nomination to go forward and I don't want my support to go to someone who succeeds. I think I have a lot to offer, but I'm afraid that it's not the right time.

Some of Johnson's supporters were surprised by his decision. Minutes before the former prime minister withdrew from the contest, the cabinet office minister wrote an article in support of Johnson.

He transferred his support to Sunak after hearing the news.

Sunak's campaign is not taking anything for granted, according to a spokesman. Before nomination papers go in tomorrow, Rishi will be talking to colleagues to discuss how to unite the party and take the country forward.