That the Labour party in Scotland has become estranged from its core supporters is beyond any reasonable dispute. It now occupies a rung below a Conservative party that is so right wing a call to tax food banks to kickstart the economy would not be deemed unreasonable.

Yet, until last week’s party conference in Perth, we didn’t know that the Labour party had also become detached from reality. This is a party that once defined itself by its commitment to social justice and fighting inequality. At last week’s conference, though, it was clear that to get ahead in this organisation you must prove how intensely you dislike the SNP.

This irrational and unhealthy obsession with Scottish nationalism was epitomised in a grotesquely ill-advised speech by the mayor of London, Sadiq Khan, which was leaked in advance of his appearance. In this, he equated support for Scottish nationalism as tantamount to racism. Khan normally strikes you as a sure-footed and wise fellow who knows more than most what it is like to prevail in the face of racism. But he was unhinged last week. These are the words he used: “There’s no difference between those who try to divide us on the basis of whether we’re English or Scottish and those who try to divide us on the basis of our background, race or religion.”

Khan rowed back slightly from this nonsense during the speech itself, but the damage had been done and its intended purpose achieved. The following day, Kezia Dugdale, Labour’s Scottish leader, was involved in one of those car-crash television interviews where the inquisitor has his subject squirming as they try despairingly to defend the indefensible. The theme of Khan’s speech was taken up with gusto by writers in the New Statesman and the Guardian, which made you think that this will become a common refrain during the second referendum on Scottish independence.

Essentially, the narrative boils down to this: “OK, we’re not saying you’re all racists but, you know, Sadiq has a point when he talks about division and all that sort of thing.”

Except, well… it’s just that he doesn’t. Indeed, Khan’s presupposition that Nationalists are trying “to divide us on the basis of whether we’re English or Scottish” isn’t even remotely true either.

There are currently more than 400,000 English people living and working in Scotland. When the terms and conditions of the first independence referendum were being discussed in 2013 the question of non-Scottish participants arose. This was a very short discussion. All people living and working in Scotland at the time of the referendum would have a vote. Nor would there be any rules on periods of residency. This was a decision that Professor Tom Devine, the nation’s foremost historian, has since hailed as “the right and moral thing to do”. He also cited this when he told the Herald on Friday: “There is unambiguous evidence that the SNP is in no way, shape or form a racist party.”

Sadiq Khan and Scottish Labour and the leftwing intelligentsia in this country can’t really be serious about this. The day after his Perth conference speech, the mayor of London was sending his congratulations to Pakistan on the anniversary of its successful struggle for independence. Presumably, too, he doesn’t believe that the American Wars of Independence was racially motivated. Are all nations who seek self-determination and to control their own destiny to be regarded as divisive and racially questionable?

As Nicola Sturgeon comes under increasing pressure to fire the starting gun on a second independence referendum, a more honest critique of SNP attitudes would focus on the tendency of some Nationalists to suggest Scottish exceptionalism. This holds that Scotland is called to a higher standard of fairness and equality and that we are a beacon of social justice and inclusiveness to the world. This is also full of holes, but it’s a long, long journey from that to holding ideas of racial superiority. And well the unionists know it.

So what’s it all about, Sadiq? Defenders of the union are searching for motifs that will denigrate the movement for Scottish self-determination. The theme that nationalism equates to racism looks like replacing those rolled out during the first referendum and subsequently discredited.

They launched Project Fear to convey several other myths and fantasies about the cost of separation that included the spurious (threats to pensions), the blatantly untrue (threat to membership of the EU) and the bizarre (no more Dr Who). They developed the fiction that the referendum itself was deeply divisive and might drive a wedge through families and communities. The Electoral Reform Society begged to differ: “We saw in Scotland during the independence referendum what can happen when people feel informed about an important decision and empowered to take part.”

Labour in Scotland has also been panicked into becoming “pound shop Conservatives”, to paraphrase Sturgeon, by seeking to portray themselves as bigger champions of the union than the party of Margaret Thatcher. They are facing annihilation in May’s local council elections and have given up winning back the multitudes of its supporters who migrated to the SNP in the wake of Scottish Labour wrapping itself in the Union Jack in 2014. Instead, they are now targeting the pro-union, working-class voters who propelled the Scottish Conservatives to recovery at last year’s Scottish elections.

Before Christmas, one senior Labour figure took me to lunch to float the idea of Labour positioning itself as ultra-unionist “just to get the local council elections out of the way”. I fear that this is now an embedded philosophy of what remains of the party in Scotland. “What about simply being a no-nonsense, no-frills Labour party fighting for social justice?” I asked him. His expression told me I might as well have been speaking in a foreign tongue.