As the turmoil over Brexit continues at a pace, Theresa May will have to fight for her political life this evening at the 1922 Committee. With pundits predicting she may well scrape through, what is the ‘22’ and what are the implications if Mrs May fails?

In order to maintain your position as leader of the Conservative Party and – if in government – to be Prime Minister you need to have the confidence of your cohort of MPs. Without it, you’re sunk.

Tracing its roots back almost one hundred years, the 1922 Committee exists to bring together backbench Tory MPs. It gives them a voice and a platform to express their views and – crucially – to decide on their leader should the need arise. Despite its name, the Committee was officially formed in 1923 following the 1922 General Election. It followed a group of Conservative MPs meeting in 1922 to vote to terminate the Tories’ coalition with the then Liberal Party, ending the government led by David Lloyd George. However, its real power came into being during the 1940s and since then it has arguably become one of the most powerful forces in British Conservative politics.

Mrs May will have to face her Commons colleagues this evening because 15% of Conservative MPs (48 in total) have written to the Chairman of the 1922 Committee, currently Sir Graham Brady, initiating a vote on her leadership, and her occupancy of Number 10 Downing Street. That threshold has been reached and that’s why the PM has a major fight on her hands.

This evening Mrs May will need 158 votes to keep her job, if she pulls it off she’s safe in the role for another year. But if she loses there will be a formal leadership contest in the Tory Party and she will not be able to stand in it. Adding to the complexity, if she survives with only with a handful of votes this will place enormous pressure on her to resign thus triggering a leadership contest to replace her anyway.

Politically, there is a huge intake of breath in Westminster at the moment. MPs who covet the top job will be watching what’s going on with beady eyes weighing up their options and potential support. Some of them are more discrete than others, politics is a rough and tumble game after all.

Given the PM’s career-defining investment in her Brexit deal a change at the top throws open an array of uncertainties, not least the shape, future and viability of Brexit as a whole. At the time of writing 104 MPs have declared for Mrs May, some way short of the 158 needed. It is, of course, a secret ballot…