The Scottish journalist Chris Deerin wrote in an article for a UK website this week: "It's a strange thing, starting to think that your homeland may be a bit dim." Strange indeed because it rather suggests that, being a member of this benighted race, you must yourself be at risk of mental infirmity.

Trigger warning! My I make my apologies in advance for the forthcoming article, which may cause offence to those with mental health issues. Perhaps, indeed, they might be wiser to skip the next 1,000 words. For the sentence above came from a widely-discussed article entitled "Scotland has gone mad".

Mr Deerin goes on: "Scotland has become a soft and sappy nation, intellectually listless, coddled, a land of received wisdom and one-track minds, narrow parameters and mass groupthink". This piece was inevitably accompanied by that picture of the beefy tattooed Scotsman with Yes plastered over his naked torso.

I wonder if this guy has ever been tracked down? His muscles must have bulged over more features on Scotland than any Scot since Andy Murray. The physique and expression seem to be a sum of all metropolitan fears about the crazies in the north who want to destroy the British way of life. Straw Dogs meets Highlander. But I digress.

Scotland, land of the Enlightenment, has, according to a number of commentators recently, lapsed into a state of collective delusion. The main symptom appears to be an inability to see the world in the way it is depicted day by day in the Daily Mail, the newspaper for which Mr Deerin writes.

The Scots, he tells us, still haven't come to terms with Mrs Thatcher's legacy. The education system has been "left to rot". The NHS is "a fat behemoth with the patient too often at its mercy".

"We have become" he concludes in true Clarkson fashion, "a land peppered with conspiracy theorists who believe in secret oil fields and MI5 plots and rigged polls, all of which is tacitly encouraged by the Nat government".

Now, there has always been a strand of cultural self-loathing in Scottish writing that goes back to the days of Boswell. There is also a healthy market for commentary that confirms metropolitan prejudices about the provinces. But this really this is a classic of the genre: the Scottish cringe elevated to a fine art.

However, I don't want to single out Mr Deerin, who is a rather agreeable individual and a good writer. The Scots-are-crazy is a metropolitan media trope that has growing steadily recently in line with polling support for the SNP.

And it doesn't apply only to Scotland. Commentary on Wales and the north of England is similarly dismissive, as if everyone who lives outside the M25 is slightly backward and devious. But the real and present danger is from the Scots.

Here's a choice cut from the Daily Express: "We are just seven weeks away from a nightmare scenario in which a minority party of ultra-left bampots and crankies will be able to dictate how the United Kingdom is governed - against the democratic wishes of the rest of us".

But they won't take it lying down. The columnist Allan Massie forecast recently that there would be "rivers of blood" flowing through England's shires if Scots were to participate in the formation of the next UK Government.

UK editors generally approach Scottish writers to express these opinions because they rightly fear that non-Scots would be accused of racism. We columnists have all been there: writing things we later regret because we thought, well, it was sort of what editors wanted to hear. Sometimes we write things that are sub-edited in eccentric ways, especially in tabloid newspapers.

And though he does tend to wander down this racial byway rather a lot, I'm sure Mr Deerin doesn't really think his countrymen and women have all gone mad. But others undoubtedly think they are no longer capable of rational thought.

Take this from Bruce Anderson "Traditionally, Scots pride themselves on hard-headedness", he wrote recently in the Daily Telegraph. "In recent years, that has often taken the form of a hard hunk of bone stretching from ear to ear inflamed by political hysteria."

I leave you to judge who is the hysteric in this case. And, once again, may I apologise to all those afflicted with this condition for the indignity of being compared to Mr Anderson. Or to Scottish expat historians like Niall Ferguson, who regularly compares Scotland to Belarus and Greece.

This opprobrium used to be heaped on the figure of "wily"Alex Salmond, who seemed to personify loony Scottishness. Portrayed as a fat tartan demagogue by cartoonists like Steve Bell, he was a figure of fun and fear at the same time. But now that he 's gone, replaced by a younger and rather sensible woman, the Scots themselves have become the object of anxious incomprehension.

Well, they must be mad, mustn't they, to be wanting to roll back to the days of tax and spend socialism. Do you know there is only one Tory MP in the whole of Scotland? And this Sturgeon woman not only wants to get rid of Trident and leave us defenceless, she wants to govern England. The cheek of it.

The odd thing about this over-wrought strand of commentary is that it invariably comes from Scottish writers who claim to be Unionists. Yet calling people mad, crazy and out to destroy democracy is hardly the best way to keep them in the Union.

Nor is saying that Scottish MPs have no right to vote freely in the Westminster Parliament. There is a widely-expressed view in the London press that, if the SNP vote down a Conservative Queen's Speech, thus bringing down the Government of the UK, it would be a democratic outrage.

Well, they'd better get ready because that's exactly what the SNP intend to do, if they have the numbers. They have no choice, because they have been elected on a pledge never to support the Tories into office; though Labour don't seem very grateful.

It is sad in some ways to see some Labour supporters participate in this demonisation of Scottish voters since it is very similar to the treatment they received from the UK media establishment in the 1980s.

Labour then was cast as the "Loony Left" for supporting things like free higher education, unilateral nuclear disarmament, increased immigration and redistribution, precisely the kind of policies that have put the SNP beyond the pale.

But here's the thing. The Scottish Labour Party appears to be afflicted by some of the same madness. Jim Murphy has been so eager to match the SNP, policy for policy, that he has even had to be slapped down by the shadow Chancellor Ed Balls for suggesting that Labour didn't support spending cuts.

The TV debates turned into a fascinating showcase of Scotland's radically different political culture to which all parties now have to tailor their message. Scots may be mad, they may be deluded, but they know what they like. And it looks as if the lunatics are about to take over the asylum.