Today the fate of the United Kingdom hangs in the balance. What polls suggested was improbable even a few months ago has now become a tangible possibility: that tomorrow these islands will wake up to find that Scotland – part of the union for 307 years – has quit the household.

A sense of destiny courses through the veins of the Scottish National Party; its vision of a new nation, a new deal, and a new freedom has won over a majority of Scotland’s young people. Hope – which propels great statesmen and incorrigible gamblers alike – has seen the Yes campaign reduce the No’s lead from 22 points to almost nothing. With most polls still within a margin of error, and given Alex Salmond’s known capacity for late surges, it may yet emerge victorious in the early hours of tomorrow morning.

If that happens, the sky will not fall in. The direst predictions – that Scotland’s leaders will bring on a depression worse that that in 1930s America – are one-sided. An independent Scotland could even, as Alistair Darling begrudgingly admitted, function as a successful country. But on questions of currency, energy, banking, defence, EU membership and more, Alex Salmond has only patchy answers – if any at all.

Bad politics

It might be assumed that, with the vote so evenly split, half of Scotland will be venomously and permanently disappointed whatever the result. That is not the case. With a “Vow” from all three Westminster party leaders laid down this week, offering Holyrood extensive powers from tax to NHS spending, even the most die-hard in the Yes camp will surely rouse themselves to put a shoulder to the wheel for Scotland – vastly more independent, if not totally so – in the event of a No vote.

A Yes, however, will leave a huge swathe of Scotland living in a country whose government was alien to their wishes. Ructions could follow. The islands of Shetland and Orkney, which lie almost as far from Edinburgh as the Scottish capital does from London, and which can lay a strong claim to North Sea oil and gas, have already signalled that they would seek greater independence from an independent Scotland.

Besides the dangers of geographic fragmentation, there are also, somewhat paradoxically, concerns over excessive unity in political affairs. Scottish politics leans heavily to the left. Only the Scottish Conservatives are ranged against four pro-statism parties. An opportunity to establish a social democratic consensus, some would say. Yet what if voters become dissatisfied? So far in this campaign, Mr Salmond has directed the legitimate frustrations of Scottish people entirely – and unfairly – at Westminster. But anti-elitism is a fickle beast; should Mr Salmond fail to deliver the promised prosperity and harmony, it could turn on him.

Poor Economics

If it chooses to use the pound but rejects close fiscal and monetary union with England, an independent Scotland would be floating itself on stormy seas indeed. The woes of the euro make clear the danger of sharing a currency and little else. By continuing to use sterling, but leaving behind the backing of the Bank of England, Edinburgh would likely have to pay more to borrow money – which would mean higher taxes and spending cuts.

Scotland’s population is ageing faster than the rest of Britain’s, and the promised revenue from oil taxes is unlikely to be enough to support it. Mr Salmond has bet big on this stream of funds; the Office for Budget Responsibility, a more reputable guide, claims it will halve to just ?3bn by 2017-18.

The skittishness of business is perhaps the most worrying factor: it has long been clear that the banks will hop over the border pronto should the Yessers come out on top; but faced with a prolonged period of uncertainty, many other businesses are likely to get cold feet. It should concern the Scottish Nationalists that a large number of voices in so-called Project Fear have come from the private sector; after all, the taxes it pays are needed to line the nest of a fledgling nation. How else are free childcare, free tuition and all the rest to be funded?

Against Nationalism

Bill Clinton, US president at a time of greater stability and peace around the world, said this week that “unity with maximum self-determination sends a powerful message to a world torn by identity conflicts, that it is possible to respect our differences while living and working together”. He is right. In the bigger picture, a divided Scotland and UK would be lesser players on the world stage; and the secession of one proud nation is likely to encourage others who seek to establish borders rather than break them down, in Catalonia and elsewhere.

We have seen, in the past few weeks, the darker side of nationalism break out in the Yes camp; the kind that brooks no dissent, that favours intimidation over conversation and that turns one neighbour against another. Naturally, passions are running high. But in urging the people of Scotland to vote No, we speak to another kind of passion: that which, on a local scale, ties together families across the border. The kind of broader fellow-feeling that reflects the United Kingdom’s best qualities: its ability to link together a vast array of peoples, without binding them down; its phlegmatic disposition; its acceptance that borders are increasingly porous in a world where money and people move freely, and the best place to stand on them is facing out, with the hand of welcome extended – not looking in, with a cold shoulder set to the future.

Tomorrow Britain as we have known it for centuries may be dead. In two years, the remaining rump could vote to leave the EU. At a time of huge upheaval around the world, it is much wiser to have the best of both worlds: more power to Scotland’s people, within a still united kingdom. Whichever way the vote goes today, post-imperial Britain is in relative decline. In an age when size matters, our country is not just better together, but in every sense bigger too.