What happens then is difficult to predict. Theresa May is keeping her own counsel but Number 10 has indicated that she will quickly make a statement to the House outlining her next steps. She has until Monday 21 January to present parliament with a motion setting out her ‘Plan B’. At present that looks likely to resemble Plan A, perhaps with further ‘clarifications’ from the EU on the temporary nature of the ‘backstop’.

But given the likely scale of defeat, it is difficult to see circumstances in which MPs – particularly her own Conservatives and the Northern Ireland Democratic Unionists – will simply change their minds if asked the same question a second time.

It is clear that the Prime Minister wants to avoid a no-deal Brexit. And any indication that the government was, however accidentally, moving towards that position would probably result in significant Cabinet resignations including Philip Hammond, Amber Rudd, Greg Clark and David Gauke. The government itself would not be able to withstand resignations of that scale and seniority and would likely collapse.

So that leaves two other options. Either the Prime Minister seeks to pivot towards Labour by committing to permanently join a Customs Union. Or she tells the Commons that because it is clear that there is no agreement, the government will seek an extension to Article 50 and pass legislation for a second referendum. Both options risk splitting the Conservative Party further and both would be accompanied by Cabinet resignations.

A divided Conservative Party – possibly permanently – may now be inevitable. By calling union leaders and accepting Labour-friendly amendments, May is already indicating that cross-party co-operation is the only way of sorting out this legislative and constitutional mess. But Labour too looks on the verge of significant splits.

The large pro-EU group of Labour MPs now see no point in supporting any version of a deal to take the UK out of the EU while they see a realistic prospect of a referendum and the chance to reverse the first vote. There is diminishing enthusiasm among many Labour MPs for an early general election, particularly since Jeremy Corbyn has made it clear that the party’s manifesto would remain committed to UK withdrawal from the EU. And meanwhile, even pro-EU Labour MPs in heavily Brexit-supporting areas such as the West Midlands worry about the backlash of overturning the first referendum.

The situation, therefore, is grim. We have a government that appears unable to win a vote on its Brexit deal, and which could not survive the victory even if it did. And we have a parliament that is unable, for the moment at least, to agree on an alternative course such as a second referendum.

That raises the spectre of a no deal crash, which is where the UK is heading if nothing else intervenes before the end of March. As this prospect nears it may yet concentrate parliamentary minds enough to clear a path that will avoid a cliff-edge fall. That would require cross-party cooperation on a scale that would fracture existing party loyalties. Yet this is already happening and regardless of how Brexit unfolds an election in 2019 is now more likely than not. The political divisions unleashed by Brexit are widening. The current parliament looks unsustainable.