Theresa May officially steps down as the leader of the Conservative Party on Friday, but will remain as British prime minister until her successor is chosen.
She announced her resignation two weeks ago, saying it was a matter of deep regret that she had been unable to deliver Brexit.
Eleven Conservative MPs are vying to replace her as party leader and, ultimately, prime minister, according to BBC.
Nominations open and close Monday.
May remains acting party leader while the contest takes place.
Meanwhile, the Conservatives fell to third place in the Peterborough by-election, behind winners Labour and the Brexit Party in second place, in what is traditionally a Tory-Labour marginal seat.
May's time as leader has been dominated by Brexit, with her party divided over the issue, and the failure to get her deal through Parliament.
The UK was originally meant to leave the European Union on 29 March but that was then pushed back to 12 April and eventually 31 October.
May replaced David Cameron in July 2016 after British voters chose to leave the EU.