LONDON, Oct 23 (AFP) - Rishi Sunak looked set to become Britain's next prime minister after Boris Johnson withdrew from the contest on Sunday, saying that although he had enough support to make the final ballot he realised the country and the Conservative Party needed unity.

Johnson had raced home from a holiday in the Caribbean to try and secure the backing of 100 lawmakers to enter Monday's contest to replace Liz Truss, the woman who succeeded him in September after he was forced to quit over a string of scandals.

He said he had secured the backing of 102 lawmakers and could have been "back in Downing Street", but that he had failed to persuade either Sunak, or the other contender Penny Mordaunt, to come together "in the national interest".

"I believe I have much to offer but I am afraid that this is simply not the right time," Johnson said late on Sunday.

The former prime minister had secured the public backing of just under 60 Conservative lawmakers by Sunday, well under half of the nearly 150 endorsements Sunak had received.

Sterling rose more than half a cent against the dollar in early trading in Asia.

Johnson's statement likely paves the way for his arch rival, the 42-year-old former finance minister Sunak, to become prime minister, possibly as soon as Monday. If confirmed, he would replace Truss who was forced to resign after she launched an economic programme that triggered turmoil on financial markets.

According to the rules, if only one candidate secures the backing of 100 Conservative lawmakers, they will be named prime minister on Monday.

If two candidates pass the threshold, they will go forward to a vote of the party membership, with the winner announced on Friday, just days before new finance minister Jeremy Hunt lays bare the state of the country's finances in a budget plan due to be released on Oct. 31.

That had raised concerns that Johnson would return to Downing Street with the backing of the party members, and not a majority of lawmakers in parliament, leaving the party badly divided. Hunt declared his backing for Sunak late on Sunday.

Some Johnson supporters could switch to Mordaunt, who has presented herself as the unity candidate, but many immediately switched to Sunak. A source close to the Mordaunt campaign said the former defence minister would continue in the contest.

"She is the unifying candidate who is most likely to keep the wings of the Conservative Party together," the source said.