How they could trigger a vote

TORY MPs wanting to oust Theresa May as party leader probably have the numbers to force a ballot – but not to actually unseat her.

Under party rules adopted in 1998, a leadership challenge will be triggered if 15 per cent of Tory MPs submit letters of no confidence.

But the Prime Minister’s critics would then require more than half of the party’s MPs to back removing her in a subsequent confidence vote.

The Conservatives currently have 315 MPs. To start a challenge 48 of them would need to write letters to the chairman of the 1922 Committee, who is responsible for overseeing the process. Sir Graham Brady, who has held the post since May 2010, is the only person who knows at any time how many letters have been sent.

Andrew Bridgen and Andrea Jenkyns are so far the only two MPs to publicly declare that they have written letters.

Should 48 letters be received, Sir Graham would stage a confidence vote in which all Tory MPs would be invited to take part.

If the leader fails to get a majority of votes, he or she resigns and cannot stand in the subsequent contest. But if they win, they are protected from facing another leadership challenge for a year.