AN SNP supporter once said to me – and he meant it – that he could tell straight away if a person was English just by looking at them. It wasn’t clear what method he used, but presumably he searched for the obvious signs of Englishness. A top hat, say. Or a monocle. Or a look in a person’s eyes that indicates a desire to talk about the 1966 World Cup.

Sadly, the guy in question wasn’t joking – he believed what he said. But a Scot who thinks they can diagnose Englishness on sight is like a Victorian phrenologist who thinks he can spot a criminal by feeling for the bumpy bits on a man’s head. It’s ignorance before logic, fear before reason. But people believe it.

I’m not saying – just so you know – that this sort of deluded, anti-English opinion represents a majority in the SNP. But it has to be there, doesn’t it? The SNP wants to sever the union with England so if you’re anti-English who else are you going to vote for? And did anyone who’s anti-English vote No in 2014? By definition, Anglophobia is going to be a thread in the SNP. More than that: it is a stratum in the geology of Scottish nationalism.

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The problem this poses for the leadership of the SNP is that the Anglophobic gases don’t stay underground; they leak to the surface and cause a bit of a stench. I’ve witnessed it myself when I’ve heard people make comments like “there are too many English in such-and-such a place”. I’ve also heard people refer many times to the “English PM” or the “English parliament”. And take a look at that banner that’s been on show in Edinburgh: “England get out of Scotland”. It’s prejudice in big letters. It’s the word “England” as a slur. It’s depressing.

However, the reaction of Nicola Sturgeon to all of this is curious. Asked about the anti-English banner during an event at the Fringe in Edinburgh this week, the First Minister said the person displaying it did not speak for the SNP. “That kind of sentiment has no place in Scotland,” she said. “People who put up banners like that, I don’t want them in the SNP.”

Obviously, this is the right thing for the First Minister to say, but the way she said it was revealing. She is prepared to condemn her supporters who are anti-English. But what she isn’t yet ready to accept, in public at least, is that nationalism itself attracts, and encourages, people who hate or distrust other nationalities and that, in the case of Scottish nationalism, this means it attracts and encourages people who hate or distrust the English.

There is a clue, though, in what the First Minister said at the Fringe to her deeper discomfort on this subject. She said – as she has before – that she does have some problems with the word “nationalist”. However, she also suggested this was because of the “global connotations” of the word – in other words, nothing to do with the SNP’s apparently friendlier version of it.

But what if the First Minister eschewed all her usual linguistical contortions over a word that sits in the middle of her party’s name and accepted that defining a movement by a nationality can create problems in Scotland just as it does elsewhere in the world? Wouldn’t that be more accurate?

But no. The First Minister can’t go there. The SNP also can’t, or won’t, really discuss the other kind of political prejudice that exists among its supporters, which is related to but different from the anti-Englishness. It’s one of the other strata in the party’s geology, sitting right next to the Anglophobia, although it’s only really been properly uncovered since the 2014 referendum.

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You’ll have seen it on social media: a Scottish person expresses support for unionism and they’re swiftly accused by Scottish nationalists of being traitors or deluded, or something to do with slavery or the Ancien Regime. Indeed, if you think the anger of some nationalists is mighty when faced with English overlords, it’s nothing compared to the anger they reserve for Scots they think are behaving like England’s servants.

Quite what you’d call this kind of behaviour from nationalists I don’t know, but I know what it looks like. It looks like political prejudice by Scottish people against other Scottish people. It also feels like a kind of chauvinism, one of the evil twins of anti-Englishness and a peculiar form of anti-Scottishness.

And to make matters worse, I’m not confident a party with the word “national” in its name is ever going to do anything constructive about the problem. But it would be a start, wouldn’t it, if the leadership of the SNP talked more honestly about the negative sides of nationalism?

They could acknowledge political history. They could discuss how humans actually behave and how words affect them and how they affect words. They could, in the end, talk honestly about what lies beneath and, more importantly, how it may influence what lies ahead.