Though Mrs May secured a temporary reprieve just last month when she won the backing of sufficient Tory MPs to head off a challenge to her leadership, the scale of the latest defeat was so overwhelming that she dared Jeremy Corbyn to call the confidence vote now being held to test if the Prime Minister has the support of Parliament.
Such a vote did bring down the government of James Callaghan 40 years ago and the ploy was last used, symbolically, on the day Margaret Thatcher resigned in 1990 when Tory civil war over Europe first broke out.
Yet these circumstances are very different. Even though less than one third of MPs backed Mrs May’s deal, any immediate change of leader, election or second referendum would inevitably require Article 50 to be rescinded, some 936 days after Britain voted to leave the European Union. It would also create even more uncertainty at a time when the country – and business leaders in particular – are demanding some certainty.
Now, just 72 days before the country’s exit from the EU, the biggest constitutional crisis since the Second World War revolves around this fundamental question: who governs Britain?
Is it the public, who voted to leave the EU and then endorsed Tory and Labour candidates in the 2017 election when both parties pledged to implement Brexit?
Is it the Prime Minister, who maintains that she is still a servant of the people looking to deliver a Brexit which is politically, economically, socially and culturally in the national interest?
Or is it the Houses of Parliament as the stand-off deepens between a coalition of Remainers who effectively want to overturn the referendum – and Eurosceptic hardliners who maintain that there is nothing to fear from a no-deal Brexit?
In many respects, it is a miracle that Mrs May has survived for so long and her EU Withdrawal Agreement deserved a kinder fate in this respect.
However the Prime Minister has not helped herself. She, and her close colleagues, have been poor tacticians, negotiators and communicators. The result is a Government, ruling party and a Parliament that have never been more split – or less capable of providing authoritative leadership. Mrs May and her team should have been reaching out to opponents from day one – and not waiting for this time of maximum crisis and vulnerability to do so.
Yet, as MPs threaten to self-combust with apoplexy, they should remember this. Mrs May does, unlike the obfuscating Opposition leader, recognise that Parliament’s duty is to uphold the referendum result – or risk irreparable damage to Britain’s democracy.
And while they have no confidence in the PM’s Brexit strategy, the coming hours will reveal if MPs do still have sufficient faith in Mrs May’ government and the electorate’s original Brexit vote.
In doing so, they need to be clear and concise – given the time constraints – on how the Government can salvage an improved deal from an inflexible European Union, a forlorn hope based on this defeat, or how any alternative approach can work in practice and break this impasse.
If not, they risk a no-deal Brexit – one scenario opposed by a majority of MPs – while, at the same time, placing Britain’s economy, and public trust in its Parliament, in even greater peril.