The sword of Damocles has finally fallen on Theresa May. At least 48 Conservative MPs have submitted letters expressing no confidence in her leadership to the backbench 1922 committee, triggering a secret ballot of all 315 MPs tonight (with impeccable timing, the Conservatives’ Christmas party is also being held tonight).

The surprise, if anything, is that it took them so long. Ever since she squandered her party’s parliamentary majority in a needless general election, May has never truly had the confidence of her MPs. Only the absence of a pre-eminent successor – and fear of the political disorder that could result – has preserved her leadership.

For the only second time in Conservative Party history, then, a confidence vote will be held in the party leader (Brexiteer Iain Duncan Smith was ousted by these means in 2003). Should at least 158 MPs – or more than 50 per cent of all votes cast – oppose her, May will be removed as Conservative leader and ineligible to stand in the subsequent contest. Should she win, she will remain in office and be granted a year’s immunity (though this does not prevent a House of Commons vote of no confidence in the government and an early general election).

Whatever the outcome, some realities will remain unchanged. Most of those Tory MPs seeking to depose May, such as Jacob Rees-Mogg and Steve Baker, wish to harden Brexit – but they have no parliamentary majority to do so. Only a softer version of May’s deal – a Norway-style agreement that keeps the UK in the single market and a customs union – could plausibly win the approval of MPs.

It is not only parliamentary arithmetic that is against the hard Brexiteers. The EU has long signalled that it will not reopen the withdrawal agreement May reached and that any deal must include “the backstop” to prevent a hard Irish border. In the absence of a new solution to the latter, the UK will indefinitely remain in a customs union. The Brexiteer dream of “Empire 2.0” – a swashbuckling Britannia striking trade deals with the Anglosphere – is being thwarted by the legacy of Empire 1.0: the Irish border.

Though Tory Brexiteers pretend otherwise, there is no better alternative available. Talk of a time-limited or conditional “backstop” is oxymoronic: the backstop is indefinite and unconditional or it is nothing.

May has played a bad hand badly – she lost her majority in an unnecessary election, she triggered Article 50 without having agreed a plan, and she carelessly alienated EU leaders – but a bad hand it always was. From the moment that she reaffirmed the Leave campaign’s pledge to avoid a hard Irish border, a softer Brexit became inevitable. None of the alleged “technological” solutions offered by Leavers have ever been credible. The Brexiteers’ true quarrel is not with May but with reality.

The removal of May as party leader and Prime Minister would force her successor to confront the choices before the UK: it can leave the EU with no deal – the current default legal outcome; it can choose a soft, Norway-style Brexit; it can trigger a general election; or, it can stage a second referendum.

All of these options, to different degrees, are unattractive: a no-deal Brexit would be one of the greatest acts of national self-harm in post-war history, a Norway-style deal would render the UK a rule-taker, rather than a rule-maker, a general election would risk another hung parliament and continued paralysis, a second referendum would intensify social divisions and further undermine the principle of parliamentary sovereignty. But before 29 March 2019 – the current legal date for EU withdrawal – Britain will have to choose one of them. May’s removal would hasten the moment at which the UK confronts this stubborn reality.