Third, if the UK is expected to give up the use of hard power, is that because no one should use it at all or because someone else should use it instead and better? Unless we buy into an impossibly sunny view of human nature and ignore the obvious lessons of history, we have to acknowledge that intractably malevolent leaders can sometimes move nation-states (like empires) to do atrocious things. And unless we’re pacifist, we also have to acknowledge that sometimes atrocious things must be stopped by armed force. Perhaps we think that the UN should do the policing — but the UN has only as many regiments as nation-states choose to loan it. No doubt a thoroughly post-imperial, “Nordic” Britain would lend its troops for peacekeeping purposes. But who, then, would fight the wars to make the just peace to be kept?

Maybe what the nationalists want is not exactly the UK’s abandonment of hard power so much as its strict submission to the collective will of the UN Security Council. If so, they would be content for the enforcement capacity of the UN to be at the mercy of the threat of veto by Putin’s Russia and the Communist Party’s China, neither of whose records of humanitarian concern are famous. They would also join Alex Salmond in condemning Nato’s 1999 military intervention to end ethnic cleansing in Kosovo as a “misguided” policy of “dubious legality and unpardonable folly”. Embarrassingly, however, this would align them against the then UN Secretary-General, Kofi Annan. It would also set them at odds with most international lawyers. Commenting on the Kosovo intervention, the leading historian and philosopher of international law, Martti Koskenniemi, has written that “most lawyers — including myself — have taken the ambivalent position that it was both formally illegal and morally necessary”.

The truth is that, in the world as we have it, the upholding of international order and the avoidance of atrocities sometimes require the naked use of armed force. That is a lamentable and tragic fact, but it is a fact nonetheless. Hard power, then, is morally necessary and we need some liberal-democratic states to be ready to exercise it. Very few European ones are willing and able to do so, however: two generations after the end of the Second World War most of them still prefer to free-ride on US power. Understandably, the Americans are getting increasingly fed-up. For Britain to take the nationalists’ preferred “Nordic” option, then, would be a major desertion of international duty and leadership, and it would probably be the last straw that broke the US’s wavering faith in Europe. The United Kingdom shouldn’t kick its post-imperial habit; it should keep it — for the world’s sake.

How to tell the unionist story (and wrong-foot the nationalist one)

The United Kingdom is good for stronger external security, for international trust and common economic advantage within the British Isles, and for a liberal international order beyond them. Complete independence for Scotland would inflict serious damage on each of these, and should be vigorously resisted. Full fiscal autonomy — for which the SNP is now pushing despite authoritative warnings of a consequent £7.6 billion shortfall in Scotland’s finances — would eventually usher in complete independence, since it would undermine British social solidarity and with it the immediate, emotional springs of felt loyalty to the UK. So that, too, should be resisted. (The signs are, however, that at least some nationalists know that they couldn’t afford what they pretend to want, so the resistance probably won’t need to be terribly vigorous.)