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Boris Johnson has solidified his front-runner status in the race to become Britain's next prime minister by gaining backing from leading pro-Brexit lawmakers.

Johnson is promising to lead Britain out of the European Union by Oct. 31, with or without a divorce deal.

Brexit-backing ex-party leader Iain Duncan Smith wrote in Tuesday's Daily Telegraph that Johnson "is the most likely to deliver on the requirement to leave the EU" by that date.

Ten candidates are running to succeed Theresa May as Conservative leader and prime minister. In votes starting Thursday, Conservative lawmakers will narrow the field down to two, who will be put to a vote of party members nationwide.

In a straw poll among some Tory lawmakers on Monday, Johnson received almost double the votes of his nearest rival.