A LEAVE vote will usher in an unprecedented period of political crisis, disrupting government, Parliament and mechanisms of rule. That’s what a number of us predicted three years ago.

That crisis shows every sign of deepening into the autumn and beyond the October 31 deadline for leaving the EU.

It is raising the possibility of an explosive clash not seen for a century between even the limited norms of British parliamentary democracy and a minority, unpopular government.

Tories rallying to Boris Johnson as the leadership candidate they think most able to claw back votes from Nigel Farage’s Brexit Party and to prevent Jeremy Corbyn entering Downing Street are not going to stem the crisis. They will accelerate it.

For “backing Boris” hits at precisely the destabilising contradiction that has wrought havoc for the governing class since June 2016.

David Cameron committed to calling the referendum in order to win back Ukip voters in 2015 and, he believed, to put to bed the generation-long Tory schism over Europe.

He told EU Commission president Jean-Claude Juncker he would win by 70 to 30 per cent.

Instead, the result of his hubris was to leave his party — most of whose MPs backed Remain — saddled with the existential dilemma of being committed to carrying through a policy that was and is flatly opposed by the majority of big business and all the Establishment and state institutions.

That fundamental contradiction lay at the heart of Theresa May’s calamity-prone administration as she tried to find a Brexit that stayed as close to the EU as possible while satisfying the hard-eurosceptic Tory right.

Her gamble in calling the 2017 election produced, like Cameron, the opposite of the intended result of a big majority that would allow her to push her Heath Robinson through Parliament.

The impossible triangle of forces that was May’s undoing is not going to end if — as is likely — the Tories again opt for a manoeuvre to counter Farage electorally by selecting Johnson.

First, there is the decoupling of the Tory Party from corporate capitalism. There was nothing short of panic from the Confederation of British Industry (CBI) and chief executives at the scale of Johnson’s victory in the first round of voting by Tory MPs.

This is a potential Tory prime minister who infamously said “fuck business” in response to capitalist opposition to a rupture with the EU.

It’s not only business. Chancellor Philip Hammond issued an extraordinary warning to all the leadership candidates that the Treasury (and by implication the Bank of England) is opposed to their assorted electioneering promises of tax cuts for the wealthy and other sweeteners.

He said that the Tories risked losing to John McDonnell and Labour their “reputation for economic management” — a reputation among the high priests of neoliberalism, it should be said.

Hammond wants the tax take on the Treasury’s spreadsheets. Even if he is probably out of a job under the new administration, the most powerful department in Whitehall has drawn a line in the sand.

A slew of former permanent secretaries and senior state figures have made the most withering interventions over the prospect of a Johnson premiership and his threat to leave on October 31 with or without a deal.

Former British ambassador to the EU Lord Kerr said yesterday: “What alarms me most about the current Conservative Party leadership race is that fiction and fantasy are back, and harsh facts again forgotten. The unicorns are back, frolicking in the Tory forest.”

That brings us to the second continuity between the outgoing May government and whatever comes next — the impasse in Parliament.

Most MPs were elected on a commitment to honour the referendum result. But the Commons comprises a majority of pro-Remain MPs.

It has a minority of hard Brexiters, a bigger minority of hard Remainers and, as convoluted voting procedures have made clear, no majority for any way forward: from a no deal exit to a second referendum.

May hoped she should could grind out a majority by repeatedly putting her deal and showing her rebellious MPs on both sides the instruments of torture: electoral wipe out and a Corbyn government.

She did achieve electoral disaster in the European Parliament elections last month. But she managed mainly to grind down her own government and any hope of finding a stable parliamentary majority.

Those essential parameters remain in place. It is an acute dilemma for her successor and more fundamentally for the British political system.

Since the Tories became a minority government, there has been periodic talk of stabilising the ship by creating either formally a national government, as in 1931, or informally through a “sensible,” pro-systemic parliamentary majority “in the national interest.”

That’s what lay behind repeated rhetoric of “Parliament taking control.” It was pitched against the democratic answer to a parliamentary logjam: to hold a general election to elect a new one (just as it was in 1931).

Many of its proponents were explicit that it might also be a mechanism for creating a new centre bloc, reducing both the Tory right and the Labour left to a rump.

The fate of (perpetual) Change UK rudely revealed reality. That has just about destroyed the “backstop” that the British parliamentary system provides for of a sufficient number of pro-systemic MPs to detach themselves from party, electorate and democratic accountability to set up a kind of parliamentary Bonapartism.

If big business lacks a political party as a reliable instrument (and Labour under Corbyn is not some Blair-Brown bosses’ B team), neither do it and the permanent state have that anti-democratic stitch-up as a plausible alternative.

A Johnson victory will deepen the impasse. Dominic Grieve and Kenneth Clarke from the hard Remain wing of the Tory Party spoke openly last week of voting to bring down his government if it careered to a no-deal Brexit.

Labour has said it will table a vote of no confidence in the new government.

That has prompted a last-ditch argument from Tory grandees either to “stop Boris” or at least box him in. It is that he and his preparedness to crash out without a deal that business can stomach will, far from averting an general election that all Tory candidates have predicted they would lose, in fact bring it about.

That the avoidance of an election is the centrepiece of the Tory leadership battle indicates the contempt for democracy.

Further, the impasse over Brexit is spilling over to a crisis of parliamentary democracy itself.

Johnson has refused to rule out the prospect touted by hard-line Tory Brexiters of dealing with the lack of a Commons majority by suspending (“proroguing”) Parliament for weeks or even months to get over the October 31 deadline without MPs stopping him.

It is an incendiary notion that has already brought condemnation from John Major and other high Establishment figures.

Doing this or anything similar would raise the crisis to altogether new levels. It would require the monarchy to use its residue of powers dating from before the English Civil War to allow a government to detach itself from Parliament to pursue a policy most people oppose.

State figures warn that it would create a constitutional crisis and undermine the ideological binding of the myth of the monarchy being above politics and the Queen as mother of the nation.

That’s their concern. It is the breach with democratic norms that should be a call to action by the labour movement.

Even without this drastic step or the threat of it, we’ve already seen a dangerous anti-democratic lurch. The last government defied all convention by boycotting votes in the Commons it was set to lose, including being found in contempt of Parliament.

When its central policy was defeated three times, May refused to resign and call a general election.

The justification was explicitly that Corbyn had to be stopped, so the people could not be allowed to vote. That was also the stated motivation of the leaders of the campaign for a second referendum, despite invoking popular democracy.

And it is this — the now deepening conflict between popular democracy and continuing Tory minority rule — that should animate the most enormous campaign by the labour movement in and outside Parliament.

Brexit and the democratic ascendency of Corbyn in the Labour Party have produced this crisis.

But it is now way beyond that and is raising questions normally suppressed in Britain — who rules, are we a democratic country, and what would real democracy look like.

A wheeze by Cameron three years ago has opened a Pandora’s box and thrown one stabilising mechanism of the governing class after another into the shredder.

The fight for a Corbyn government is now becoming the fight for democracy against arbitrary rule through authoritarian methods and arcane procedures going back to Henry VIII.

Not just a fight for a new government, but for even the modest parliamentary democracy people have taken for granted for decades.

That is a potentially explosive combination in the next few months.