UNDER Tory rules, Theresa May will face a vote of no confidence if 15% of the party’s MPs write a letter to Graham Brady, the chairman of the party’s 1922 committee of backbenchers.

The Tories currently have 315 MPs, so 47.25 of them would need to write to trigger a contest.

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Despite the protestations of Brexiteers, Brady has made clear that only whole MPs can vote, and that he must receive 48 letters.

At the moment, we know for sure that 25 MPs have posted letters to Brady. Yesterday, the Sun said there were 42 on his desk, while Sky News claimed he’d received 46.

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Once that threshold is breached, things will move quickly.

Brady will announce a vote where Tory MPs will be asked to say if they support or oppose their leader.

In 2003, when MPs tried to oust Ian Duncan Smith, the contest was held the day after the committee chairman received enough letters.

If May wins, she remains in office and cannot be challenged again for 12 months. If she loses, she’s out, and barred from standing in any leadership contest.

If, as reported over the weekend, several candidates, including Boris Johnson, and David Davis, come forward to replace her, a secret vote is then held among Tory MPs to try and whittle down the field.

The candidate with the fewest votes is removed and MPs vote again on Tuesdays and Thursdays, until only two are left.

The contest is then decided by the party’s supporters, with ballots being posted out to every activist with more than three months of membership.