Former London mayor Boris Johnson abruptly pulled out of the race to become Britain's next prime minister on Thursday, in a shock move that upturned a political order shaken by last week's vote to leave the European Union.

Johnson, whose support for the campaign to leave the EU was widely considered one of the decisive factors in the campaign, had been bookmakers' runaway favorite to succeed David Cameron, who quit last week after failing to persuade British voters to stay in the bloc.

Johnson's unexpected departure from the race, announced just minutes before the party unveiled the list of candidates, shows the speed with which the political landscape is being reshaped.