In Theresa May’s perfect world, the Withdrawal Agreement would have been carried through Parliament by Conservative votes.  It has failed to pass the Commons three times.  So she has turned to Jeremy Corbyn.

In her next best place to this ideal world, the Agreement would somehow be supported by the bulk of both the main parties.  Labour would settle for a customs union which isn’t called a customs union but really is a customs union – in addition to the customs union already written into the Withdrawal Agreement, at least as far as any future Unionist government is concened.

Meanwhile, Corbyn would stop pushing for what he can’t have – namely, guarantees that Labour-style future employment and environmental policies will be proofed against a fundamental of our unwritten constitution: that no Parliament can bind its successors.  Instead, the Prime Minister would offer vague assurances.  Meanwhile, Corbyn would block his party’s push for a second referendum.

May would thus be able to wangle a short extension from the EU at today’s emergency summit – having persuaded Angela Merkel and Emmanuel Macron that she and Corbyn will shortly combine to drive the Withdrawal Agreement through the Commons.  This would then happen.  A Bill based on the Agreement would pass swiftly.  Plans for British participation in the European Parliamentary elections would be scrapped.  Britain would leave the EU before May 23.

Her Party would then forgive her for preparing for those elections; for whatever losses emerge from the local elections on May 5, and for all the trials, U-turns, humiliations, defeats and tribulations of the Brexit negotiation process.  She would thus have room to execute a swift reshuffle in which her most likely successors would be moved sideways, marooned or sacked.  There would be talk of bringing on a new generation of leadership candidates – to reinvent the Party for the future, along the lines which Onward and others are floating.

Meanwhile, the Prime Minister would move on from the Withdrawal Agreement to the Political Declaration.  She would kick off the Brexit talks, Part Two, by reviving parts of her Chequers plan.  She would enjoy a last hurrah at the Conservative Party Conference, before December arrived with its prospect of a confidence ballot.  But by then she would have so befuddled her critics and confounded expectations that the ballot might not take place at all.  She would be able to stay on for just a little longer…

But it takes only a moment’s though to perceive all this as the fantasy that it is.

May will surely not be granted a short extension.  If the EU does not somehow plump for No Deal – which is improbable – she will be given a long one, with terms approved by Angela Merkel and Emmanuel Macron.  British participation in the European Parliamentary elections will loom.  Corbyn is unlikely to come to her rescue.  If he does, the logic of her turning her back on her own Party, and approaching Labour instead, will work its way to completion.  Most Labour MPs would vote for the Withdrawal Agreement.  Many Conservative MPs would not.

Whether it passes or fails, the Parliamentary stage would be set for further seizures of power by the Letwin/Cooper axis, aided and abetted by John Bercow.  The natural drift of the Commons would then be towards a second referendum.  There is an outside chance that some form of Norway Plus scheme may revive.  We would be on course for a softer Brexit, or else for No Brexit at all – unless the voters seem ready to put two fingers up to Britain’s pro-EU ascendancy.  In which case, expect talk of revocation to grow louder.

This takes us to the crunch.  Ten Conservative MPs voted in favour of cancelling Brexit at the start of this monthEight backed a second referendumA hundred and eighty-seven opposed an extension in March: that number represented two-thirds of the Parliamentary Party, and included six Cabinet Ministers.  In these circumstances, confronted by revocation or a second referendum or even Norway Plus, the Tory Party could split altogether.  It is not impossible to imagine Corbyn winning a no confidence vote and the election that followed.

There is an alternative, but it is neither pleasant, easy, nor guaranteed to work.  In a nutshell, it is to use any long extension to remove Theresa May as leader of the Conservative Party, and hold a leadership contest that would conclude after those wretched European elections.  (Since were that new leader in place for them, he or she would get off to the worst possible start.)

In the event of the Withdrawal Agreement having failed to pass, this new leader would want to begin all over again.  He would propose a policy based on that set out in the Brady amendment – the only Brexit policy option for which the Commons has recently voted – and built on in the Malthouse Agreement by Nicky Morgan, Steve Baker, Damian Green, Simon Hart and others.

He would thus be backing a lower alignment rather than a higher alignment policy.  In the event of the Withdrawal Agreement failing to pass, it would also make sense for the backstop to be put in place for a limited period while “alternative arrangements” are thrashed out.  This is more or less what the recent legal elaborations agreed with the EU point towards.

If the EU rejected this approach, there would be No Deal.  You will point out that there is no clear majority in the Commons for it.  This is correct.  Which is why this new leader would have to prepare for a general election later this year in any event.

Yes, such an approach risks some Tory MPs peeling off to the Independent Group – though, as we say, an approach based on the Brady amendment makes sense, since the whole Parliamentary Party, pretty much, was able to unite behind it.

But the alternative risks a bigger split, both in the Commons and among the grassroots, in any event.  Expect soon to hear a new form of that old talk about a Conservative-UKIP alliance – this time round, of a Tory-Brexit Party pact.

Furthermore, there is even more at stake than the future of the world’s most venerable political party: namely, whether the referendum verdict of 2016, carried by the largest vote in this county’s political history, is to be upheld or dishonoured.

You will have spotted the fly in this unpalatable ointment.  Namely, that the Prime Minister is unwilling to go.  The 1922 Committee Executive has presented her with the obligatory glass of whisky and pistol.  She has refused to pick them up.

Furthermore, there is no formal means of expressing no confidence in her leadership until December.  The habit of suggesting indicative votes in catching on.  But the 1922 executive is very doubtful that these could produce a resolution.

That leaves the Cabinet.  Its members are divided on policy, dogged by personal ambition, and daunted by the scale of the challenge before them.

To ask this dispirited band to come together, tell the Prime Minister to step down as Party leader, and stay in Downing Street until the ensuing leadership election is concluded – particularly when the options are so grisly – is a very big ask indeed.

But the driver of the car is taking it towards the edge of the cliff.  True, it may crash if the Cabinet attempts to wrest control from her.  But if they don’t, it is set to career into the void, in any event.