At least 48 Conservative MPs have called for a vote of confidence in Prime Minister Theresa May, triggering a secret ballot on Wednesday evening.
In a speech in front of 10 Downing Street, May said she would contest the vote “with everything I have got” and warned a new prime minister would be faced with “delaying or even stopping Brexit”.
Under Conservative Party rules, once 48 letters of no confidence in the party leader have been sent to the chairman of the 1922 Committee Graham Brady, a confidence vote is automatically triggered. It is unclear how many letters beyond the 48 have been sent as the number is kept secret by the committee.
The secret ballot vote will run for two hours from 18:00 GMT and the result is expected before 21:00.
Theresa May needs to secure the votes of 158 MPs to survive, a simple majority of sitting Tory MPs, but if she only wins by a small margin she may not feel she can continue to lead the party and resign. Margaret Thatcher won 54.8% (204 votes) in a confidence vote in 1990, but still resigned shortly afterwards.
So far, 174 Tory MPs have publicly expressed support for May to continue as PM, but as the vote is a secret ballot, it is unclear how many of these MPs will follow through on these promises in private. At least five senior ministers are rumoured to have publicly supported May, whilst privately saying they will vote against her.
If May loses the vote, a Tory leadership election will be launched, which could last for several weeks and could put significant pressure on the Brexit timetable. Even if May wins the vote, it is unlikely her Brexit deal will pass parliament and the weakened PM will find little support from opposition benches.