A small piece of fissile material has been quietly passing its way around Westminster. Discreetly deposited where MPs could pick it up without fuss or fanfare, the blandly-worded document contains a framework for the most explosive constitutional crisis in almost three hundred and seventy years.

Briefing paper 8589 from the House of Commons Library has been winging off the shelves as MPs and aides avidly digest its contents with a mixture of incredulity and alarm. It is entitled Prorogation of Parliament. The cause of the alarm is that this–the shutting down of Parliament in order to push through a no-deal Brexit–is precisely what the likely next Prime Minister refuses to rule out as an option.

The prospect is regarded by many MPs as little more than what Boris might call “bunkum.” Nobody, surely not even Boris, would dare perform such a constitutional outrage, one which would, gods forbid, risk “dragging the Queen into politics.” Tory MP Dominic Grieve, a former Attorney General who has pulled out all the parliamentary stops to block a no-deal Brexit, warns that “democracy may not survive” such circumstances. There have been warnings that police will have to drag protesting MPs from their clutches on the Commons green benches. 

To others, on all sides of the House, the true horror lies not only in the consequences of a forced parliamentary shutdown but the fact that any putative Prime Minister could even contemplate an act more associated with dictators in far away lands. If he has so little regard for Parliament at the start of his tenure, where else might a Boris premiership lead?

His allies brief that it is all part of the “steel” required to make Brussels buckle, that it is simply to ensure no ramp is closed off on the road to exit. Yet the fact that such an august institution as the Commons Library has deemed it necessary to produce this “what if” scenario is testimony to the seriousness with which the possibility is regarded.

Former Prime Minister John Major has threatened a legal challenge against Boris Johnson if he tries to remove the right of Parliament to block a no-deal exit. And anti-Brexit campaigner Gina Miller–whose 2017 action resulted in the Supreme Court ordering the Government to allow MPs a decisive vote in the process–has already assembled a legal team to prevent a Boris shutdown.

Opposition to crashing out is the only position which commands a clear majority in the Commons. A clear majority against what MPs in all parties fear would be the worst of all outcomes for Britain, its economy, trading prospects and global status. This is represents the biggest obstacle between Parliament and Boris’s ambition.

Legal and constitutional experts shake their heads gravely and say prorogation will never–can’t ever–happen. It would, as Ms Miller’s lawyers have said in a letter to the putative PM, be “contrary to fundamental constitutional principles” and “seriously undermine parliamentary sovereignty.”

The team at Mishcon de Reya, the firm which also acts for the Queen, says it would be “closing the doors of Parliament to prevent it from legislating on the most important political issue of the day.”

Yet Johnson, given the chance over and over again in TV debates and interviews, persists in sticking to the line that he will not rule out the biggest constitutional upset since Charles I challenged the power of Parliament in 1642. That, as history records, didn’t go well for him in the end.

So why does King Boris keep open such a dramatic path to what many see as an impossible promise–to ensure the UK leaves the European Union by 31 October? It is, in his own words, “do or die”.

His allies argue that he is simply leaving all options open in order not to box out any room for manoeuvre; that he will be able to secure a new deal before the deadline. Voices from Brussels say differently. The new head of the European Commission, the arch-federalist Ursula von der Leyen, has already ruled out further renegotiation of the Withdrawal Agreement. As far as the majority of the leaders of the other 27 countries are concerned, Britain has effectively already left. They’ve moved on.

The Commons Library paper makes it clear that “there is no obvious legal mechanism by which Parliament could prevent its exercise (prorogation) otherwise than by passing legislation to constrain it.” What is unclear is precisely how a divided Parliament could do that or, even if there were a plan, whether there would be time before we reach the 31 October cliff edge.

The most definitive move would be for MPs to revoke Article 50 which enshrines the deadline in law. But that, to Brexiteers, would be a blatant betrayal of the referendum mandate. Von der Leyen has hinted that yet another extension–a massive failure for Boris–might be possible “for a good reason.” It is accepted that the only good reasons would be a UK general election or a second referendum.

One Tory MP, James Gray, a fervent Brexiteer, believes by-passing Parliament should be seen as part of normal business. “Prorogation is not some devilish plot to allow Brexit through, or scupper it,” he says, “it is an essential part of the Parliamentary drum beat.”

An increasing number of MPs who don’t go with that beat expect there to be another extension. But further delay would be a grave failure for the new Prime Minister, who made exit by Halloween the centrepiece of his campaign. Others see a general election arriving sooner rather than later.

Faced with existential discord in Labour and the opportunity to outdo both the Brexit party and his own Remainers, Boris might just be tempted to to call a “do-or die” election himself.

Just days before Britain gets a new PM we have no idea where this country, its Parliament and its people are headed. Having tied himself in a political knot out of which there appears no obvious escape, one suspects this is just as true for Boris as the rest of us.