THIS week, let’s play a little game of “who said that?” Man is a forgetful animal, but even by ordinary human standards of misplacing your past arguments and misrecalling what you once thought and said and did, Scottish politics is suffering from a catastrophic case of amnesia.

You may not find newsprint wrapped around your fish supper these days, but old news and spent convictions seem remarkably disposable in our political culture. George Orwell wrote that “to see what is in front of one’s nose needs a constant struggle”. But to remember what was once in front of your nose seems even harder, and too many of our political reporters seem disinclined even to try.

Interviewed by Iain Dale this week, John McDonnell told an Edinburgh Fringe audience that it was “for the Scottish Parliament and the Scottish people to decide” whether there should be another referendum on Scottish independence. The shadow chancellor went on that “we would not block something like that. We would let the Scottish people decide. That’s democracy. There are other views within the party but that’s our view.”

When McDonnell’s remarks hit the headlines, the Labour right hit the roof. Their analysis was as wild as it was predictable. McDonnell’s mild recognition of the principle that Scottish self-determination should be expressed through democratic votes for Scottish institutions was immediately characterised by Edinburgh South MP Ian Murray as a “rant” which “betrays our party’s values”. But what values are these?

Joining Murray in taking a pop at McDonnell, Douglas Alexander contrasted McDonnell’s principled position with a nostalgic fairytale of his party’s history. “The Labour Party of Smith, Cook, Brown and Dewar,” Alexander said, “knew that, as democratic socialists and internationalists, our responsibility is to oppose nationalism, not enable it.”

This superheated rhetoric goes well beyond the – perfectly legitimate – desire for Scotland to remain part of the United Kingdom and a Labour policy of refusing to support such a poll in the Scottish Parliament. It creates instead a new and nakedly undemocratic purity test, where the only unionism which counts for anything is one which demands Scotland’s future in the UK should never be revisited, no matter what a majority of Scottish parliamentarians or the Scottish public vote for.

Despite superficial appearances, this is not an expression of political confidence. And despite what Murray maintains, it is not in the Labour Party’s best democratic traditions. The Labour right in Scotland seems to have lost the language of self-determination and are now putting all their emotional labour into pretending they never played footsie with Scottish nationalism in the first place.

But the historical record speaks for itself. In 1989, every single Labour MP in Scotland – save for the reliably thrawn Tam Dalyell – put their name to a modern Claim of Right which acknowledged “the sovereign right of the Scottish people to determine the form of government best suited to their needs, and do hereby declare and pledge that in all our actions and deliberations their interests shall be paramount”.

By signing this political declaration of the sovereignty of the Scottish people, with its national analysis and explicitly nationalist overtones, were Gordon Brown, and Donald Dewar, and Alistair Darling “betraying Labour party values”?

Try another quote on for size. Who said this? This Tory administration is “governing Scotland without a shred of mandate” and that “to all intents and purposes, Scotland is an occupied country in which the ruling power depends for its support on a power-base which is outside the country”.

Perhaps Jim Sillars in a Govan stump speech? Alex Salmond in the House of Commons? Try again. It was Labour stalwart Robin Cook back in 1983. The comment was not happily received by all of Cook’s pro-devolution Labour colleagues – but it gives the lie to the idea Labour’s argument for devolution was a nationalism-free project.

Certainly, you don’t need a national analysis to explain federal structures in a country. Gaze across Europe and the world and you’ll find countless instances of provinces, states and regions, enjoying limited autonomy from the central government. But the United Kingdom is, frankly, not like other states. Its devolution is not structured like Germany’s federal republic, or Canada, or the United States.

Like the political demands which drove its creation, devolution in the United Kingdom has always been articulated and justified in an explicitly nationalist framework. To borrow the usual industrial cliches, if there isn’t a fag-packet between the wants, needs and desires of the workers on Tyneside and Clydeside, why have a Scottish Parliament at all? What is the rationale for devolution, and why did the Labour Party devise its institutions along national lines in Wales, Scotland and Northern Ireland?

Labour’s attempts retrospectively to delegitimate this are as strange as their insistence that the only way you can really be an internationalist is to stick with Britain, whatever the British state actually does, however inimical to co-operation across borders the United Kingdom actually proves.

Predictably enough, McDonnell’s remarks were also leapt on by commentators as a gift not only for the SNP, but for Ruth Davidson, presenting another opportunity to push the line that Labour “can’t be trusted” with the Union. After a period of anguished silence in the wake of Boris Johnson’s entry into Downing Street, the Scottish Tory leader seemed glad of the distraction, taking to Twitter to say she feels “for those Labour voters that stood side by side with major figures of their party and against the forces of nationalism in 2014. Know that the Scottish Tories will always stand up for our United Kingdom.”

But the idea that McDonnell’s comments are a boon for the deflating Scottish Tory leader are premised entirely on having the memory and inquisitorial attention to detail of a common mayfly, because, as recently as July 2016, Davidson herself expressed precisely the same democratic sentiments McDonnell articulated in Teviot’s Gilded Balloon.

In the aftermath of the Brexit vote, Davidson opposed holding a second independence vote – as is her right – criticising the proposal as “premature” and “further destabilising in a period of instability”. But when pressed by Gordon Brewer about whether Downing Street should block such a poll, Davidson was happy to make a merit of the fact she had “never said it should be denied”.

She told BBC Scotland: “I would argue as strong as I could that we should stay part of our biggest market and closest friend. Constitutionally the UK Government shouldn’t block it, no.” Does this make Ruth Davidson “soft on the Union” too? Was she failing to “stand up for our United Kingdom”?

When David Mundell sat down for a post-P45 rumination this week at the Fringe by the Sea event in North Berwick, telling Katy Balls that if a “Scottish Parliament election is fought explicitly on the issue of another referendum, and then there is a majority of nationalist parties, then evidently you do have to listen to that”, does that mean the former Secretary of State for Scotland’s British patriotism should be questioned too?

In a week of coverage focused almost entirely on tactics and optics and internal factionalism, the fundamental question of principle at the heart of this was lost.

McDonnell was right. If Scottish independence is a legitimate political aspiration, as both the Labour and Conservative parties have accepted for generations, those parties cannot choke off every legitimate route for the democratic expression of that view. The confrontation between the United Kingdom and is spiralling disunity can be delayed – but it cannot be deferred forever.