BORIS Johnson, a prominent campaigner for British withdrawal from the European Union, says he will not be a candidate for leadership of Conservative Party.
Mr Johnson said he did not believe he could provide the leadership or unity needed.
Johnson's decision means Justice Secretary Michael Gove and Home Secretary Theresa May are front-runners in the race.
They and others will compete to succeed Prime Minister David Cameron.
The winner of the contest, set to end in September, will become prime minister and play a vital role shaping the nature of Britain's relationship with the European Union after last week's Brexit vote upended Cameron, whose bid to keep Britain in the EU block failed.
The bookies' early favorite is May, who is seen by many in the party as a safe pair of hands as the country struggles to disentangle itself from the EU.
"This is not a normal leadership held under normal circumstances," May said in a speech Thursday in London. "The result means we face a period of uncertainty we need to address head on."
Although May had offered a tepid endorsement of Britain's place in the European Union during the referendum campaign, she was clear that the vote would be respected.
"The United Kingdom will leave the EU," she said, pledging to create a brand new government department devoted to negotiating Britain's "sensible and orderly" departure from the 28-nation bloc.
Boosting May's chances was a last-minute falling out between her two leading competitors - Gove and Johnson - who had campaigned together to yank Britain from the EU.
In a statement, Michael Gove said he would pursue the prime minister's post after concluding that Johnson "cannot provide the leadership or build the team for the task ahead."
Gove had been expected to back Johnson and stay out of the race.
An email from Gove's wife, Daily Mail columnist Sarah Vine, obtained earlier by Sky News, suggested that Gove should ensure he had specific guarantees from Johnson before backing the latter's bid.
She added that influential right-wing media barons Rupert Murdoch and Paul Dacre "instinctively dislike" Johnson.
Gove's camp has declined to comment on the missive.
The opposition Labour Party is also is extreme disarray, with leader Jeremy Corbyn facing intense pressure to resign after losing a confidence vote. He has lost the support of the party's lawmakers but claims the rank and file still back him
He is expected to face a formal leadership challenge in the coming days. He has faced heavy criticism for failing to campaign effectively in support of keeping Britain within the EU.