SCHOOLCHILDREN once imagined their place in the world, with its complex networks and allegiances, by writing elaborate postal addresses. British youngsters began with their street and town (London or Manchester, Edinburgh or Cardiff), followed by England, Wales, Scotland or Northern Ireland; then came the United Kingdom (and after that Europe, the World, the Universe…). They understood that the UK, and all its collective trials and achievements—the industrial revolution, the Empire, victory over the Nazis, the welfare state—were as much a part of their patrimony as the Scottish Highlands or English cricket. They knew, instinctively, that these concentric rings of identity were complementary, not opposed.

At least, they used to. After the referendum on Scottish independence on September 18th, one of those layers—the UK—may cease to exist, at least in the form recognisable since the Act of Union three centuries ago. As the vote nears, Scotland’s nationalists have caught up with the unionist No camp in the opinion polls, and even edged ahead (see article). More and more Scots are deciding that the UK, which their soldiers, statesmen, philosophers and businessmen have done so much to build and ornament, does not cradle their Scottishness but smothers it. This great multinational state could be undone in a single day, by a poll in which just 7% of its citizens will participate. That outcome, once unthinkable, would be bad for Scotland and tragic for what remained of the UK.

The damage a split would do

The rump of Britain would be diminished in every international forum: why should anyone heed a country whose own people shun it? Since Britain broadly stands for free trade and the maintenance of international order, this would be bad for the world. Its status as a nuclear power would be doubtful: the country’s nuclear submarines are based in a Scottish loch and could not be moved quickly. Britain would also be more likely to leave the European Union, since Scots are better disposed to Europe than are the English (and are less likely to vote for the Conservatives, who are promising a Euro-referendum if they win next year’s general election). The prospect of a British exit from the EU would scare investors much more than a possible Scottish exit from Britain (see article).

The people of Scotland alone will decide the future of Britain, and they are not obliged to worry about what becomes of the state they would leave. But—perhaps not surprisingly, given the endurance and success of the union, imperilled though it is—Scots’ own interests, and the rest of Britain’s, coincide.

At the heart of the nationalist campaign is the claim that Scotland would be a more prosperous and more equal country if it went solo. It is rich in oil and inherently decent, say the nationalists, but impoverished by a government in Westminster that has also imposed callous policies. They blame successive British governments for almost every ill that has befallen Scotland, from the decline of manufacturing industry to ill-health to the high price of sending parcels in the Highlands. Alex Salmond, Scotland’s nationalist leader, is broad in his recrimination: Labour and the Tories are of a piece, he suggests, in their disregard for Scotland.

But Scotland’s relative economic decline is the result not of southern neglect but of the shift of manufacturing and shipping to Asia. If Westminster has not reversed all the deleterious effects of globalisation and technology, that is because to do so is impossible. The nationalists know this, which is why, sotto voce, they would continue many of Westminster’s policies. Instead they make much of minor adjustments, such as abolishing the “bedroom tax”, a recent measure designed to nudge people out of too-large social housing. To break up a country over such small, recent annoyances would be nuts.

The nationalists’ economics are also flawed. Scotland would not, in fact, be richer alone. The taxes that would flow to it from the North Sea would roughly compensate for the extra cost of its lavish state, which would no longer be funded by Westminster (last year spending was some £1,300 per person higher in Scotland than elsewhere in Britain). But oil revenues are erratic. They would have earned Scotland £11.5 billion in 2008-09 but only £5.5 billion in 2012-13. If an independent state were to smooth these fluctuations by setting up an oil fund, it would have less cash to spend now. In any case, the oil is gradually running out. In order to maintain state spending after it is gone, taxes would have to rise. And a crunch might come much sooner. Foreign investors and big businesses that mostly serve English customers could well move south.

Westminster has ruled out a currency union (see article)—correctly, given that the nationalists propose a deficit-widening fiscal splurge and that the assets of Scottish banks are an alarming 12 times the country’s GDP. It might relent, but only if Scotland agrees to such strict oversight that independence ends up meaning little. The nationalists say that kinks over currency and the like could be worked out amicably—that it would not be in Britain’s interests to antagonise its new northern neighbour, particularly since (they hint darkly) Scotland could refuse to take on its share of the national debt. They are far too sanguine. If Scotland goes, the rest of Britain will be furious, both at the Scots and at their own leaders, who will be impelled to drive a hard bargain.

Mr Salmond is on stronger ground when he argues that if Scotland does not leave Britain it might be dragged out of the EU against its will. This is indeed a danger, but in going independent Scotland would swap the possibility of an EU exit for a certain future as a small, vulnerable country. Its best hope of remaining influential is to stay put, and fight the Eurosceptics.

A lot to lose

In the end the referendum will turn not on calculations of taxes and oil revenue, but on identity and power. The idea that Scots can shape their own destiny, both at the referendum and afterwards, is exhilarating. Yet Scotland already controls many of its own affairs (even if Mr Salmond’s Scottish National Party, which runs the devolved government and is driving the Yes campaign, has not done much with its powers so far). Moreover, as Westminster politicians of all stripes have hastily made clear, if Scotland votes No, the devolved administration will soon get so much clout that the practical difference between staying in the union and leaving it will narrow. That would also lead to the distribution of power away from Westminster and to other bits of Britain, which should have happened long ago.

So by staying in, Scots will not just save the union but enhance it, as they have for 300 years. For the UK, with all its triumphs and eccentricities, belongs to Scots as much as it does to the English—even if increasing numbers of them seem ready to disown that glorious, hard-earned heritage, and to simplify their identities by stripping out one of those concentric rings. That goes against both the spirit of this fluid century—in which most people have multiple identities, whether of place, ethnicity or religion—and the evidence of the preceding three. For all its tensions and rivalries, and sometimes because of them, the history of the union shows that the Scots, Welsh, English and Northern Irish are stronger, more tolerant and more imaginative together than they would be apart.