Many words can be used to describe Dominic Grieve, but “spinmeister” certainly isn’t among them.  He is a very old-fashioned politician – a QC, model of propriety and the son of an MP himself – who was formed in the pre-Blair age.  So when he said last weekend that “we could collapse the Government”, he was calling the consequences of today’s vote as he sees them.  If Theresa May agrees with him on any point, it is on this one.  “We cannot accept the amendment on meaningful vote agreed in the Lords,” her spokesman said yesterday, adding that it would “allow parliament to direct government on its approach to exiting the EU, binding the prime minister’s hands and making it harder to secure a good deal for the UK”.

“Making it harder” is a euphemism.  Views differ on the consequences of MPs trying to run the negotiation with the EU themselves, rather than hold Ministers to account for their handling of it.  Some think that this would make stopping Brexit likely, as the natural pro-Remain majority in the Commons asserts itself.  Others believe that it would make a no deal Brexit happen, since the Government and the Commons won’t be able to come to agreement, and time is too short to prevent or postpone leaving the EU.

But either way, there is no disagreement about the main consequence of a Government defeat on the Grieve amendment today.  If it is passed, May will lose what control of the Government’s side of the negotiation she now has.  Consequently, the EU side of the table will have no reason to come to terms with her.  It will simply be able to sit back, wait for Commons control to kick in, watch the ensuing confusion, and hold out a solution that MPs comprehensively rejected last week – EEA membership.  It is not beyond imagination that, as the Commons thrashes in a quicksand of incoherence, EU negotiators make a dramatic offer – to call off Brexit altogether, in the expectation that a broken-spirited Parliament bends to their will.

The logic of events suggests that Theresa May would be gone before that point.  A majority of Tory members already want her out before 2022.  It is very hard indeed to find a Conservative MP who disagrees in private.  Not rated by Tory Brexiteers, and now not trusted by hardline Remainers either, a defeat today would lose her the little room for manoeuvre that she has already, in a Commons in which her party has no majority.

And not just on Brexit.  Yesterday, Sajid Javid and Jeremy Hunt ignored her reservations about a full review of legalising the use of cannabis for medical purpose, and the Home Secretary announced one anyway.  Philip Hammond says that the extra NHS spending is a one-off.  Try telling that to Gavin Williamson, who wants more money for defence, and has the Commons backing to get it.  Or to Javid, currently the master of all he surveys within the Government, who wants more cash for the police. Or to James Brokenshire, who has Conservative local authorities knocking on his door.  Or to Damian Hinds, who can remind Downing Street of the damage that protesting heads, other teachers and parents did to the Tory vote a year ago.

On the economy, on Commons votes – on almost everything – that quicksand would swallow May up.  But a change of leadership would leave the fundamentals unaltered.  A Prime Minister Gove or Hunt or Javid or Johnson would go to the Commons to find the numbers exactly as May left them.  On Brexit, the clock would still be ticking and the talks would have been suspended – since, during a leadership election, there would be no-one for the EU to negotiate with.  The drumbeat of Project Fear would quicken to a frenzy.

The only coherent solution would be for the new leader to seek a general election – which, notwithstanding the Fixed Terms Parliament, he or she could doubtless find a way to, as May did last summer.  So we come to the vice which Grieve’s amendment, if successful, will apply to the Conservative Party’s vitals.  Tory MPs have no real confidence in May, but a replacement would offer no respite.  They don’t want a general election, but a paralysed Government and Parliament would make one all but unavoidable long before 2022.  And voters take their cue on snap elections from Brenda from Bristol.  The danger for the Conservatives would be punishment in consequence.  A poll would also pose a terrible question to Ministers: why didn’t you prepare for a No Deal Brexit next March?

The British people don’t want Prime Minister Corbyn.  But could voters in this circumstance be blamed for concluding that there was no alternative but to roll the dice and give him a chance?  True, logic isn’t everything in politics.  Sometimes it is very little at all.  Maybe if Grieve’s amendment is passed today, the Government will limp on until 2022.  Do unhappy Conservative MPs really want to chance it?  Less than a day will pass before we all find out.