But resistance alone is not enough; saying “No” will not suffice. Nor will saying “No” with better reasons than “Yes”. As indicated last January by Nicola Sturgeon’s resort to quasi-religious confession in the face of hostile economic facts, Scottish nationalism’s power is fuelled by a spiritually intoxicating brew of political idealism, moral purism, and self-righteous scapegoating — the same brew that kept alive the revolutionary flame in Irish breasts a hundred years ago, despite the absence of objective injustice. For sure, it remains important to keep on fingering the nationalist vision’s sincere naivetés, less-than-honest inconsistencies, and unjust slander, for, as penitent Islamists testify, the best way to undermine a political fanatic’s faith is to sow seeds of doubt and confusion and then allow time for the penny to drop. But it’s always much easier to leave, if one has somewhere else to go to. So unionists need to develop and broadcast a positive story about the Union, articulating the ground beneath our feet and bringing back to common consciousness all the things it’s good for. A sustained and nationwide public discussion is needed to let such a story gather momentum and take to the air. While professional integrity would prevent the BBC itself from telling the story, it could nevertheless occasion it by staging a series of national conversations about Britain’s constitutional future. If a more urgent public service is needed right now, I don’t know what it is.

But unionists need to do more than talk; we also need to show. Whenever the European Union funds a project, it advertises it for all to see, loudly and proudly, on billboards. The United Kingdom should start doing the same. Since many Scots appear to have forgotten what the UK does for them, the UK needs to remind them. What’s more, since many Scots have never set foot in England, let’s take up Adam Tomkins’s proposal and twin every schoolchild in Scotland with one in England and pay for them to visit each other and learn each other’s ways. And how about strengthening communication across the Union by building, if not bridges, then railways, and extending HS2 beyond Manchester and Leeds to Glasgow and Edinburgh?

And since the future of the Union now lies primarily in its hands, it is vital that the Conservative government add substance to its talk about “One Nation”. If it isn’t true that George Osborne’s planned tax credit reductions will seriously hinder some of the poorest and most vulnerable among us, then the government must say so and explain long and loudly. And if it is true, then it needs to have the courage to admit it and adjust the policy. Otherwise the Tories’ reputation as the “nasty party” — nowhere stronger than in Scotland — will only deepen, the appearance of a widening gulf between political cultures north and south of the border will only thicken, and the nationalist story’s plausibility will only grow.

If the United Kingdom is to survive — and it would be a tragedy for all its peoples, and for other peoples too, if it didn’t — then its virtues need to be asserted and broadcast and demonstrated in ways that any citizen can appreciate. More than half of Scots are still appreciative and hungry for encouragement, support, and leadership. Behind recent electoral appearances and Alex Salmond’s smokescreen many others lie open to persuasion. So go on, Mr Cameron: seize the initiative and deploy the resources of your government to show us what the Union’s good for.