When Theresa May was in the commons defending her draft deal, all the talk was about whether or not more ministers would resign or whether she could get this Brexit through Parliament.
But that is a way off: there is a more immediate calculation that those around her are running. The first numbers to watch are not how many ministers she loses, but how many of the letters of no confidence have been sent to chairman of the 1922 Committee Graham Brady.
To bring down a sitting Conservative leader, the party’s MPs need to initiate a no confidence vote. This happens when 15 per cent (48 MPs) of Tory MPs write to the party’s 1922 Committee Chair.
Brady would then schedule a vote, in consultation with the party leader. Last time such a vote was triggered, when the Conservatives were in opposition in 2003, it was scheduled the day after the threshold of letters was reached. It will happen within days.
MPs then vote either in support of or against Theresa May. If 50 per cent of all Conservative MPs vote in support of her – that’s 159 MPs – she stays as leader, and no new vote against her can be triggered for 12 months. She would remain as PM, and her own party would have no internal mechanism to bring her down. This would strengthen her hand; but it would not alter the broader challenge of getting this deal through Parliament, and surviving as a government without a majority.
If more than half her MPs vote against her, May would have to resign as Conservative leader. A new leadership contest would be triggered in which any candidate could stand. She would still temporarily be PM until she resigns, or until a new leader is elected.
However: if May lost such a vote she could choose to resign in favour of another Conservative MP who would temporarily be PM. This would cause significant complaints from Labour, who would argue that the government have no majority and the Queen should call on Corbyn.
It would also be difficult for any temporary PM. The UK has no mechanism for this scenario. A new PM would have all the powers of the role, but would have far less authority.
The UK has de facto caretaker governments during general elections, but not during leadership challenges. During election campaigns, the incumbent government are not supposed to initiate major new policy, negotiate any major deals and so on. If the government needs to act, it is supposed to ‘consult’ with the Opposition. But this is nothing more than constitutional habit.
So if a leadership challenge is initiated, and if May failed to win 50 per cent the conservatives, we are in tricky territory. Should tory MPs unite behind a leader to avoid this constitutional quagmire? What does it mean for continuing negotiations? What does it mean for legislation? They might want May to stay on until a new leader is chosen – but this might not be until after Christmas and certainly after the December EU Council meeting. What would happen to existing policy in the meantime is a difficult question.
And all this is before you get into the politics of what any future Conservative leader candidate might pitch as their own proposed path for future policy. All of this might be the in the minds of those thinking which way they would jump if the leadership no confidence vote is called.
Dr Catherine Haddon is resident historian at the Institute for Government.