It’s a long-established canard of Scottish nationalism that shadowy forces south of the Border are seeking to undermine or even “destroy” Scotland’s distinctive identity and institutions.

Perhaps the classic statement of this rather paranoid worldview came from the late William McIlvanney in a lecture to the 1987 SNP conference. Never before, he claimed, had a government been “so determined to unpick the very fabric of Scottish life”.

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Margaret Thatcher, he added, took the “axe of her own simplicity to the complexities of Scottish life” and, if she were allowed to continue, would “remove from the word ‘Scottish’ any meaning other than the geographical”.

Now at the time, few (and that includes many Scottish Labour and Liberal politicians) would have disagreed with those sentiments, but looked at from a distance it’s largely hyperbolic. Like many, McIlvanney considered heavy industry intrinsic to a sense of Scottish self, but the decline of coal-mining, steel-making and ship-building were hardly specific to Scotland.

In fact, most distinctly “Scottish” aspects of public life were not only undisturbed by Thatcherism but in some respects strengthened. In opposing (in theory more than practice) its economic reforms, the Kirk, STUC and so on were all given a new lease of life, as was the cultural world to which McIllvanney contributed so much.

It was striking, therefore, to discover that for all the supposed development of Scottish nationalist “thought” over the past 30 years that this paranoia is still just beneath the surface. Nicola Sturgeon kicked things off with an almost embarrassingly tenuous speech to the David Hume Institute, claiming that after 20 years of “progress”, devolution was facing a “grave threat” from a “powerful Westminster faction”.

That faction, of course, had probably “never fully embraced devolution”, and therefore saw Brexit as an “opportunity” to “rein in” the Scottish Parliament, clawing “back ground” in order to usurp “multinational United Kingdom democracy”.

Despite the fact that no one has bothered identifying the “faction” nor what they want to claw back (beyond some EU powers that don’t currently rest with Holyrood), this grievance narrative swiftly took root online, in certain newspaper columns and, of course, with SNP MPs and MSPs ever keen to parrot whatever new official line emanates from the Dear Leader.

Last week it reached a bizarre crescendo when a silly column by a consistently inflammatory Times columnist was seized upon as proof by otherwise sensible political observers that there was indeed a concerted push by London to revert to a “unitary state model”, whatever that might mean.

Melanie Phillips’ column, as I said, included some daft arguments, not least its claim that Ireland had a “tenuous claim to nationhood” having only seceded from the UK in 1922. But aside from a simplistic reading of what defines a “nation” and therefore “nationalism”, there was no suggestion that the UK should scrap its devolved legislatures in Cardiff, Belfast and Edinburgh.

No one, other than some hard-line Scottish Tories, advocates doing that, yet the First Minister has created a “power grab” narrative (repeated by Alex Salmond in a recent interview) that’ll no doubt linger until the next independence referendum, if not beyond. That it has little basis in empirical reality doesn’t really matter, the whole point is to play to tribal fears of wicked Tories doing nasty things to Scotland.

Ms Sturgeon also implied that the “multi-national” nature of the United Kingdom was under threat, as if somehow the pre-1997 British state was unitary in nature. In truth, it was never that simple. For much of the 18th century the newly-constituted Great Britain left Scotland pretty much free to govern itself within a broader macro-economic framework, while after the other Act of Union in 1801, Ireland retained a separate executive (if not a legislature).

In 1885, meanwhile, a bipartisan Liberal/Conservative Bill created a Scottish Office and associated Cabinet minister, both of which acquired greater powers, autonomy, cash and clout over the following century. In 1964, a Welsh Office was added to the mix, while for half a century Northern Ireland enjoyed virtual fiscal autonomy via its own (Stormont) parliament and prime minister.

The political scientist Professor James Mitchell has long questioned “unitary” accounts of the UK, as much a myth as the oft-repeated narrative about the “sovereignty of the Scottish people”. A few years ago he reached the conclusion that rather than being a “unitary state”, the UK was better described as a “union state”, in that it was a composite of different unions, each of which had taken care to preserve distinctive characteristics of its component nations.

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Conservatives used to be good at articulating this more nuanced view of the Union (or rather Unions), and indeed Theresa May’s recent speech to the Scottish Conservative conference made a point of contrasting a UK which had “passed more powers down to its constituent parts” with a European Union which had “sought to centralise more power in Brussels”.

The Prime Minister then added an interesting caveat, arguing that devolution mustn’t mean “we become a looser and weaker union”. For too long, she said, the “attitude” in Whitehall had been to “devolve and forget”. Now Mrs May didn’t actually go on to explain what she meant by that, but it remains a huge leap to assume it indicated a concerted effort to “claw back” powers from Holyrood.

To repeat, the paranoia rests on Westminster rather than Brussels exercising powers over agriculture and fisheries. Last week the SNP MP Stuart McDonald said it was “increasingly clear” the Conservatives were planning to “undermine and roll back” devolution by taking control of powers that ought to go “directly” to Scotland and Wales. Not only that, but there was a possibility of them reopening the original Scotland Act in order to “strip powers” away from Holyrood.

As ever, this reduces a complicated issue to simplicities. Not only are the powers in question “shared” rather than the exclusive preserve of Edinburgh, London or Brussels, but the Scottish Government should be careful what it wishes for. Does it really want responsibility for providing Scottish farmers with often-generous subsidies? And besides, on acquiring these powers, it then wants to hand them back to Brussels. Anyone would think an “anyone but Westminster” attitude guides the SNP in this respect.

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The argument used by William McIlvanney wasn’t new even in 1987. Forty years earlier the Scottish Unionists (or Conservatives) had accused a Labour government of “de-nationalising” Scotland, centralising in London autonomy previously exercised north of the border. Such an argument undoubtedly resonated, but that didn’t – and indeed doesn’t – make it right.