After every shattering bungle, some PR creep says: “Lessons have been learned and appropriate changes put in place.” Well, and British Brexit? What lessons, and what hope for changes?

There’s one obvious lesson which Westminster, despite centuries of dire experience, still fails to learn. Do not kick Irish cans down the road. Some contain Semtex. All have a way of rolling back and tripping you up. There’s an English habit of not thinking about Ireland lest it spoil a nice afternoon. If David Cameron had thought of the British border in Ireland, he would have called his referendum off. But he kicked Arlene Foster and two Irish taoiseachs down the road. Now British politics lies sprawling on that same hard tarmac.

The House of Commons includes repulsive opportunists, bone-headed pedants and a few real scoundrels. But most MPs are well-meaning men and – especially – women. Yvette Cooper, wise Joanna Cherry, Anna Soubry the maenad with blazing eyes: they and their sisters have been the stars of these awful weeks. Best of all, none of them did that “womanly” number of trying to mediate between gnashing, stomping males. They gnashed too, and with a furious clarity. And it was Nicola Sturgeon who gave Theresa May the smartest epitaph: “The only leader in modern times who tried to fall on her own sword and managed to miss.”

The next lesson from this disaster engineered by well-meaning folk is that the machine has broken down. This is because it wasn’t built to take the strain of minority governments. Contrast the Scottish parliament after 2007, elected by a “continental” proportional system, where Alex Salmond kept an SNP minority government in power for its full term by dexterous bargaining. Why the difference? The difference, that is, apart from Mrs May’s astonishing deafness to dialogue. First, because the Anglo-British non-constitution is archaic. Incredibly, nobody knows what the law of state is. Where is final authority – in the sovereignty of parliament (a weird old doctrine), in the “peoples’ vote” by a referendum or in the “executive”, the cabinet claiming to embody the royal prerogative? In this fog, the 2017 election left a minority government unable to steer a divided house composed mostly of Remainers: MPs and even cabinet ministers who were pledged to honour the referendum result but didn’t really believe in what they were doing.

Second reason for the difference: the Westminster power machine is still heavily authoritarian. In parliament, it has operated through the massive majorities created by “first past the post” voting. This conceals the fact that “parliamentary sovereignty”, in the narrow local sense that the Commons could order a government about, has mostly dwindled to myth. The Brexit struggles with Mrs May’s minority administration have been horribly revealing. They show how far executive power has crept forward in recent years, to the point at which the Commons can only wrest back control over its own agenda by cunning and ambush.

This week’s effort by MPs to bypass government and construct a new Brexit policy out of informal cross-party alliances might succeed. But Mrs May, instead of backing one of these initiatives in order to save her own Brexit deal, tried to strangle the whole process at birth. She failed. But it was a bad omen. Would this democratic taking-back of control by the house survive under the next majority government? Unlikely, if it’s a Tory one.

When a government is weak, it’s obvious that small – even tiny – groupings inside and outside the main parties gain monstrous leverage. Most of them have ancestry. The European Research Group is only the current incarnation of Tory Europhobia, which itself carries genes from the League of Empire Loyalists, a small but pompous choir in the 1950s. The 10 Democratic Unionist MPs, who don’t even represent majority opinion in Northern Ireland, took Mrs May’s bribe to keep her in power and then, last Friday, stabbed her in the backstop.

When trying to shift the basalt flagstone that is Mrs Foster's mind, Mrs May intones her mantra: 'This precious, precious union ...'

Significantly, the long-lasting splits in British middle-class parties have been about issues (the Corn Laws, Irish home rule, imperial preference, Europe) rather than ideology (class war, religious identity, equality). This is because, in pragmatic old Britain, ideas are easier to compromise than printed manifesto promises.

When trying to shift the basalt flagstone that is Mrs Foster’s mind, Mrs May always intones her mantra: “This precious, precious union of ours… ” You hear it when anyone points out that England, not Britain, voted to leave the EU. For her, it’s the union that is precious. Not Ulster or Wales or Scotland, places – the last especially – about which she knows little and cares less beyond their capacity to make bother. Her union is somewhere else, a precious badge of office that Britain’s prime minister is trusted not to lose.

But the union is genuinely in trouble. It’s not only that Brexit is wrenching Scotland out of Europe against its will (62% Remain). It’s becoming clear that the 1998 devolution settlement only remained stable – only made sense – in the context of British and Scottish EU membership. Westminster and Holyrood shared some of their powers with Brussels, not just with each other.

To some extent, that masked the gross asymmetry that threatens the whole arrangement – the fact that England has 85% of the entire UK population. But now London asks: what’s the point of returning agriculture powers from Brussels to Scotland? Much more convenient to keep them here and create a single British farming system. Already, the “joint ministerial council” meetings – the devolved ministers with their Whitehall equivalents – are shrivelling towards a ritual in which the “British” members read out the agenda and then edge towards the door.

“Precious union”? Here, as in so many other ways, the Brexit upheaval has shown that British governance is becoming more authoritarian, less spontaneous, more blindly provincial in its indifference to the real world outside. In the darkness under the Palace of Westminster, there lies a gigantic, swelling fatberg of undemocracy.