Like Theresa May before him in 2016, Boris Johnson has made the journey to Scotland very early in his prime ministership. Johnson went north this week to try to show how much he cares about what May called “our beloved union” and what he characteristically calls the “awesome foursome”. Like May, Johnson did this not because Scotland is inscribed on his heart, but because Brexit is threatening to revive the clamour for Scottish independence. If ever there was a case of trying to shut the political stable door after the horse has bolted, this is it.

It is conceivable that, in 2016, a more flexible politician than May might have managed to reach some kind of accommodation with the Scottish parliament in the aftermath of the Brexit vote. It would, of course, have been a very tall order to persuade the nationalist-led government of a country that had voted strongly to remain to weaken its commitment to the EU. But if May had offered to devolve some powers direct from Brussels to Holyrood, had pursued a soft Brexit that kept Britain in the EU single market, and had not made an end to free movement a non-negotiable part of her stance, it is possible – no more than that – that the mood in Scotland might not have shifted towards independence in the way it has now begun to do.

But these are might-have-beens. We are three years down the track. The UK is hurrying towards the European exit. And those putative pill-sweeteners are certainly not offers that Johnson is remotely interested in making anyway. On the contrary, the overriding aim of his embryonic prime ministership is to drive Britain out of the EU in three months’ time, under more or less any terms he can. During his visit to Scotland he confirmed that he was pushing £300m into previously announced “growth deals” with the devolved nations. But this is tantamount to trying to reapply an already worn-out sticking plaster to a limb broken in many places. It doesn’t stick and it does not deal with the main problem.

The main problem is that “the ties that bind our United Kingdom” as Johnson put it this week are being casually sacrificed on the altar of Brexit. Johnson, as the high priest of the Brexit cult, is not in a position to do much to slow the deepening fracture between Conservative England and its opponents, even if he really wanted to, which he shows no real sign of doing. Johnson is a man who does not care about Scotland at the head of a movement that doesn’t care about Scotland either. It is little more than a month since a YouGov poll revealed that around two thirds of the Conservative party membership – the same people who have made Johnson the prime minister – want Brexit to happen even if it does serious damage to the economy, even if it breaks the Tory party in two, even if it means Northern Ireland leaving the United Kingdom, and even if it means an independent Scotland.

It hasn’t helped that the Tory party enjoyed a limited recovery in Scotland since 2016 under a leader, Ruth Davidson, who is a strong remainer. The election of Johnson, and the new prime minister’s refusal to keep her ally David Mundell in the cabinet as Scottish secretary have pulled the rug out from under Davidson.

The principal political beneficiary of all this is Nicola Sturgeon. Her Scottish National party has single-mindedly and remorselessly spent most of the past decade blaming the English Tories for everything. Sometimes they have been right; at other times wrong. Yet the UK government’s determination to deliver a hard or no-deal Brexit has finally begun to deliver a new Scottish mood into the SNP’s welcoming arms.

Scottish opinion polls this year show a marked shift since 2018 towards support for independence among Scotland’s remain voters. Johnson, who is easily presented as a quintessentially entitled southern English politician, may well give this shift a further boost. The fact that the prime minister chose to head straight to the Faslane nuclear weapons base to make his pitch suggests that he has little interest in wrong-footing the many stereotypes on which the SNP plays so effectively. The ties to which Johnson referred may have bound the UK together for centuries. Now, though, those ties are fraying faster than ever before.

• Martin Kettle is a Guardian columnist