What happens if Theresa May loses her no confidence vote

• There will be a vote of confidence in Theresa May's leadership tonight.
• Half of Conservative MPs need to vote against the prime minister to depose her.
• Here's how the leadership contest will work - and what happens if she loses.

LONDON - Theresa May is facing the prospect of a leadership challenge after 48 Conservative MPs sent letters to the 1922 committee, triggering a vote of no confidence.

Conservative MP Graham Brady, the committee's chairman, said a ballot will be held between 6pm and 8pm tonight in the Commons.

"The votes will be counted immediately afterwards and an announcement will be made as soon as possible in the evening," Brady said.

Here's how the leadership contest will work.

1. May addresses 1922 committee

At 1700 UK time, Theresa May will address the 1922 committee which is comprised of all backbench Tory MPs. She will tell wavering MPs that replacing her would risk a Jeremy Corbyn-led Labour government and inevitably mean that Brexit was delayed.

2. A ballot is held

Between 1800 and 2000 UK time, MPs will vote in the House of Commons either to support or oppose Theresa May, marking a black cross on a piece of paper with two options - confidence or no confidence.

Key point: It required only 48 MPs, or 15% of Tory MPs, to trigger a vote itself. But it would require a simple majority of 158 - half the Conservative MPs plus one 50% of MPs - to depose the prime minister.

3. If May wins?

She remains prime minister. But if she won by only a slender margin she could feel pressured to resign.

4. If May loses?

Theresa May is no longer leader of the Conservative party. She would be forced to resign as prime minister. A leadership contest would then be held. The likes of Dominic Raab, Sajid Javid, and Boris Johnson are seen as frontrunners to replace her if that happens.

5. If there's a leadership contest?

Graham Brady would select a date for the first round of the leadership contest, in consultation with the outgoing Theresa May. Contenders to replace her must first gain the backing of two other Tory MPs. Depending on how many candidates there are, there would be rounds of elections, and MPs with the fewest votes would drop out of the race.

6. And then... Once there are just two Tory MPs left, Conservative party members will be able to elect one of them. Graham Brady would announce the winner. That person would become the prime minister.

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