The Scottish Tories’ Achilles' heel is back. In truth, it never goes away; it simply lurks, niggling, threatening, always ready to cause maximum damage at the worst possible time.

And so it did last week on a day of chaos for Jackson Carlaw’s party, starting with the resignation of Scotland Office Minister Douglas Ross MP, followed by a succession of extremely senior MSPs breaking cover, followed by a ramping-up by Mr Carlaw.

The Achilles' heel is the Conservative Party in London. The topic, on this occasion, was the Dominic Cummings saga. It doesn’t really matter, though. It’s always something.

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Time and experience has also told us that it doesn’t really matter who the Scottish Tories’ leader is. David McLetchie’s ferocious intelligence and forensic skills were not enough to create any significant electoral shift. Annabel Goldie, as likeable a person as you’re likely to meet, could not detoxify the Tory brand. Ruth Davidson, as strategically talented as she was counter-intuitive, managed a significant electoral breakthrough, but did so by ruthlessly exploiting the rejuvenated brand of unionism and relegating the ‘C’ word. And now Jackson Carlaw, smart, quick, effective in Parliament and approachable. He has identified real pressure points for Nicola Sturgeon – education and tax, primarily – but he has zero chance of becoming first minister next May which is, after all, the point of all this.

That is, of course, the saddest part. Because for all that the SNP governments of what will, by May 2026, be nearly 20 years have been broadly competent, as a citizen it would be nice to think that at some point we might be able to replace them.

The cold reality, friends, is that we cannot, because the next party of government in Scotland does not yet exist. Indeed, I think 20 years of devolution has exposed the historic error that was made by all Westminster parties when they imposed themselves as fixtures in the Scottish Parliament.

Where might we have been with a Canadian party structure? Mirroring that model would have seen the Conservatives, Labour and the Liberal Democrats stand in Scotland for Westminster elections, but leave a clear path for a set of new, independent parties to stand at Holyrood. Scottish parties. Parties which never look over their shoulder.

For it is that – the look over the shoulder for guidance and approval from Westminster – which has allowed the SNP to be "Scotland’s party"; to play three-versus-one to devastating effect.

There are people – the "ultras" – in the Scottish Tory party who will argue that black is white. They are utterly unable to see a change in party structure through anything other than the prism of the 2014 independence referendum. If there is not a single UK political party, so the theory goes, then there cannot possibly be a single UK country. But as well as being primarily the view of the sort of hysterical person who wears a Union Jack tie every day, it bears no relationship to reality.

Scotland has, after all, managed to maintain a separate legal system, education system, church, football team, flag and so much else for the last few hundred years without the walls falling in. Why should a political party structure be any different?

It certainly isn’t in Canada, where the Assemblée Nationale du Québec, perhaps the most analogous to Holyrood, is currently governed by an anti-independence party with no relationship to Ottawa’s federal parties, with the Liberals (no relationship to their federal namesakes) running second and the pro-independence Parti Québécois in third.

Indeed, Québec is the least of Ottawa’s worries, with most fearing that if Canada is to suffer a secession it is likely to be the oil-rich Albertans, tired of subsidies, waving goodbye.

In 2011 Murdo Fraser MSP (disclaimer: with my help) made the only serious attempt to change the Scottish Tories’ unsatisfactory relationship. He opened his launch speech with the words: “Albert Einstein said the definition of insanity is doing the same thing over and over and expecting a different result.” But his members said no.

And if the Scottish Tories act true to form, last week’s wailing and gnashing of teeth will subside. Someone will take Mr Ross’s job, the discontent in Holyrood’s MSP office block will subside and all will return to normal.

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Until the next time. And there will always be a next time.

I know Jackson Carlaw well. I consider him a friend. I know what his words mean, and I know what his facial expressions mean. He is angry. Angry with Boris Johnson. Angry with Dominic Cummings. And he’ll be angry, again, the next time.

What should he do? One, use his influence to ensure Mr Johnson delivers a Brexit deal which works for Scotland. Two, get through the Holyrood election, with fingers crossed. Then, three, get the hell out of this political party.

• Andy Maciver is Director of Message Matters.

All columnists are free to express their opinions. They don’t necessarily represent the view of The Herald.