The Staggers 12 December 2018 Whether May wins or loses, what will the confidence vote mean for Brexit? It’s only 107 days away, by the way. Getty Sign UpGet the New Statesman's Morning Call email. Sign-up Theresa May is facing a vote of no confidence in her leadership of the Conservative Party tonight. First, a brief reiteration of the rules as they stand: to survive, Theresa May simply needs a bare majority of Conservative MPs to vote confidence in her – that’s 158 MPs. There are no other candidates at this stage: it’s just a ballot paper asking Conservative MPs if they have confidence in her. If she loses, it triggers a full-blown contest in which she cannot be a candidate. If she wins, she is immune to further challenges for a year – so if May survives tonight’s vote, she is safe in post until 12 December 2019. In 1990, Margaret Thatcher stood down despite winning the first ballot – but back then the rules were completely different. Leadership challenges were triggered by MPs challenging the leader, and candidates needed to command both an absolute majority of MPs and a lead of more than 15 per cent over their challenger, in that case Michael Heseltine, in order to avoid a full leadership challenge in which others, not just the challenger, could stand. Thatcher stood down in order to avoid a defeat in the second round and the emergence of other challengers to her leadership. The rules are so different now that trying to take lessons of what happened to Thatcher to what might happen to May is about as useful as applying the lessons of Labour’s old electoral college. If May wins by one vote, she will hang on until the bitter end. The question is, will she win? We’ve always known that there were enough disgruntled Eurosceptics to trigger a confidence vote in May’s leadership Michael Heseltine – but there have never been enough of them to win one alone. So it’s significant that, as I wrote in greater detail last night, there is a shift in the Tory mood among middle-ground opinion in the parliamentary party. There are some suggestions that she could increase her chances of survival by promising to stand down after 29 March 2019 if she wins, but the problem is that Conservative MPs remember that May promised MPs in marginal seats that she would not call an election in the 2016 leadership election, and broke that promise less than a year later. (Resentment over that is part of why middle-ground opinion is curdling against her.) The big question of course is not what this means for who leads the Conservative Party but what it means for Brexit. The Prime Minister is right this morning to say that whether she wins or loses, the parliamentary arithmetic and the political imperatives of the 27 other member states of the European Union will not change. There is no harder negotiated Brexit available than the one agreed by May. But if Theresa May loses tonight, it triggers a leadership election in which the incentive for every candidate will be to pander to the Tory party membership. There are certainly more than seven pro-European Conservatives who might, if it looks as if a no-deal Prime Minister is planning to control the legislative timetable and prevent a negotiated exit, vote to trigger an election. But there’s no guarantee that the next parliament will be anymore able to unite around a Brexit deal than this one and it could simply return a pro no-deal Prime Minister to office. If May goes down in flames, the prospects of a negotiated exit from the European Union may well go up in smoke with her. › Some NHS trusts are spending as little as £238 on cyber security training Stephen Bush is political editor of the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to domestic and global politics. Subscribe For more great writing from our award-winning journalists subscribe for just £1 per month!