ast Thursday’s debate will have little impact in England. Scotland is another matter. Nicola Sturgeon’s performance has made it inevitable that there will be a constitutional crisis in North Britain and that we will be arguing about Scottish independence for the foreseeable future. Even the French ambassador’s (disputed) account of her apparent attempts to manipulate the balance of power at Westminster will not damage her.

La Sturgeon was effective: clear, confident, combative without being shrill. One could add a fourth “c” word: cold. It is less a question of a splinter of ice in her heart, as a few scraps of heart tissue clinging to an icicle. She has all the human warmth of a

tricoteuse waiting for a tumbril. But that was not so apparent during the debate. There is an irony. If she had given such a display as a Labour politician, she would now be the strong favourite to succeed Ed Miliband. As it is, she has expunged any prospect of a Labour recovery in Scotland.

Up to now, although Unionists reeled with every successive Scottish poll, there was some ground for hope. Surely the Nats could not keep up this level of intensity? After all, there were still five weeks to go. But Ms Sturgeon has supplied fresh momentum. The journalist Claud Cockburn said that the average Irishman was three double whiskies ahead of the average Englishman in political consciousness. In recent months, a similar claim could be made about Scotland. But Nicola Sturgeon does not sound as if she has spent too long in the pub. Her down-to-earth tone will help to hide the fact that the underlying economics are nonsense. “Our Lassie showed the English what for,” the Nats will be saying this weekend. There may not be time for the hysteria to subside.

The Scottish public mood is extraordinary. Over the past few months, millions of Scots have been baying at the moon. The most bizarre fantasies have not only circulated; otherwise sane people have given them credence. There are supposed to be massively valuable oilfields whose existence the English are concealing. Though that is about as plausible as Enoch Powell belonging to a satanic cult, it is now part of everyday discourse.

The Nat rumour machine also claims that there are large new oilfields to the west of Shetland. But there are three problems with that. First, oil companies have been prospecting in that area, without success. Second, if oil was found, it would be in rough seas. At anything like current oil prices, extraction would not be economic. Third, if Scotland were to secede, Shetland might try to opt out. Those are easy points to make. Scottish friends of mine have been doing so on the doorstep – and getting nowhere.

How can this be happening? The Scottish Enlightenment represented the triumph of rationalism, always in a calm and restrained fashion. Its philosophers and economists believed in using reason to improve the human condition, not to reshape human nature. They virtually invented free enterprise; they elevated Scotland to the intellectual leadership of Europe. In a splendid setting, the Castle on one side, the sea on the other, their contemporaries laid out the New Town. Calm, rational and beautiful buildings: it is the Enlightenment as architecture.

While it would be absurd to claim that every Scot has read Adam Smith, there were grounds for believing that Enlightenment values had influenced the Scottish character. Keynes poked fun at socalled practical men, dismissive of theories, who were actually in thrall to some long-dead economist. If that economist had been Scottish, the thraldom would be benign.

Scots came to think of themselves as shrewd, canny, hard-headed. They persuaded much of the world to accept them at that valuation: a nation of Dickson McCunns. Where is the canniness now?

It was undermined by three historical developments. First came the end of the British Empire. Not only was it often a job-creation scheme for Scots. When both nations could take pride in being part of something much larger, small Scotland was less inclined to feel resentful of its larger neighbour. Once a Royal Duke lowered the final Union Flag, it was easier for malcontents to claim that Scotland was England’s last colony. (Those sentiments are expressed in characteristic language during the film Trainspotting, much the most depressing portrait of Scotland ever written or broadcast.)

There followed the inevitable decline of heavy industry. Two generations ago, most Scots lived within 50 miles of a steelworks, a shipyard, a coalfield – or all three. A lot of Scots regarded that as part of their economic birthright. This came to a rapid end. But it is unfortunate that Margaret Thatcher was prime minister in the final phase.

It was not her fault that globalisation had changed the terms of trade. Indeed, on any sensible audit of the Thatcher years, Scotland should regard her as a benefactor. Silicon glen, financial services, oil and gas: Thatcherism created the conditions in which the new industries could flourish. But no credit came her way. Her voice did not help; it set many Scottish teeth on edge. That was a childish reaction: there was a lot of childishness about, encouraged by both Labour and Nationalist politicians. It suited them to pour abuse on her and her party, to turn Toryism into political toxic waste.

So there was a quarter of a century of demonisation, which drove economic common sense out of Scottish public debate. By the end, many young Scots had come to believe that Scots’ values were superior. Scotland stood for social solidarity, and indeed socialism. It stood for the public sector, not for private enterprise. Mrs Thatcher and her English capitalist friends hated the Scottish ethos, which is why they had set out to destroy the Scottish economy. This brainwashing explains why Nicola Sturgeon will have earned huge applause in Scotland for attacking Ed Miliband from the Left. Scottish Labour helped to sow the dragons’ teeth, never expecting that the dragons would turn on them. They ken the noo.

Not since the Thirties has a once great nation been in the grip of so many delusions. This is malign thraldom, and it is not clear how it can be ended. Nicola Sturgeon and her party are on the side of Trainspotting Scotland, not Enlightenment Scotland. Yet there is no sign of Scotland coming to its senses.