Sir Graham Brady, the chair of the 1922 Committee, has received at least 48 letters from Conservative MPs calling for a vote of no confidence in May. Under party rules, a contest is triggered if 15% of Conservative MPs write to the chair of the committee of Tory backbenchers.

A ballot will be held on Wednesday evening between 6pm and 8pm, Brady said, with votes counted “immediately afterwards and an announcement will be made as soon as possible”. Sources said an announcement could be made by 10pm.