The head will decide Scotland's future At the turn of this year, David Cameron chose to pick a fight with Alex Salmond, the nationalist first minister of Scotland who has often cowed Westminster and Edinburgh alike with his warranted reputation for political guile. The prime minister demanded an early referendum on Scottish independence. Mr Salmond, needing time to win his compatriots to his cause, scolded him for "Thatcher-esque" meddling. Even unionists worried that the intervention of a Conservative Englishman would turn wavering Scots against them. Seemingly, the opposite has happened. As the two men met in Edinburgh yesterday to sign off the details of the plebiscite, which will take place in the autumn of 2014, the visitor must have felt more confident than the host. There is little to suggest that support for independence has grown beyond roughly a third of Scots, where it has been for decades. Some polls show that it has fallen this year, though much depends on the phrasing of the question. In a less quantifiable way, Mr Salmond seems more of a political mortal than he has in recent years. Mr Cameron represents a calibre of competition that the first minister does not face in his own backyard. Many unionists who felt bleak about the future of the UK a year ago now radiate a confidence that borders, foolishly, on insouciance. The reason behind their momentum befits Edinburgh, the great city of Enlightenment. Unionists have so far appealed to voters" heads far more than their hearts. Mr Cameron was implored by many this year, including some of his own advisers, to run a romantic campaign. He was urged to invoke 300 years of unionist history, the many battles fought by Scottish and English soldiers under the same flag, and the jarring notion that friends and relatives divided by the border would - if Mr Salmond got his way - officially become foreigners to each other. But this counsel misunderstood Mr Cameron, who has a very English preference for the tangible over the emotional. It also misread Mr Salmond's weakness. The first minister is a sublime politician and an able administrator but he struggles to explain away the practical obstacles to Scotland going alone. This is why so many Scots vote for him without backing him on independence. Above all, the romantics in Mr Cameron's ear rather missed the point of campaigns, which is to win over the undecided. There are plenty of heartfelt unionists in Scotland but they are already certain to vote to remain part of the UK. The referendum will be decided by voters who are neither unionists nor nationalists in principle; people who are open to pragmatic arguments in either direction. Last year's Scottish social attitudes survey found that views on independence depend enormously on its perceived economic impact. If it made Scots £500 a year better off on average, independence would be favoured by 66 per cent to 21 per cent. If it made them worse off by the same amount, Scots would vote against it by a similarly strapping margin. Sure enough, Mr Cameron has ignored the high-minded advice and instead painstakingly ground down the nationalists on matters of economic substance, especially the question of which currency an independent Scotland would use. If it kept the pound, as Mr Salmond claims it could, then its interest rates would continue to be set in London. Its other options are joining the less than enticing euro or creating a currency of its own. There have been other tough questions, such as whether an independent Scottish government would be liable if Royal Bank of Scotland needed rescuing again, but the currency conundrum has done more than anything else to keep the nationalists at bay. Even the unionists" choice of unofficial frontman embodies their practical approach. Alistair Darling is the least lyrical of politicians - certainly no match for Mr Salmond as a conjuror of stirring visions - but the former Labour chancellor of the exchequer brings a forensic command of economic issues. If Mr Darling is the unionists" main asset, Mr Salmond's is time. Having won his struggle with Mr Cameron over the timing of the referendum, he has two years to campaign. Economic conditions are now inhospitable for the nationalist message: recession creates a fear of risk and the euro - the currency Mr Salmond once favoured - is still fighting for its future. By 2014, it is just conceivable that both the economy and the euro will be robust. It is likely that Mr Cameron will be even less popular than he is now, giving Mr Salmond something to define himself against. Supporters of the status quo and of independence are outnumbered by those who want more powers for the Scottish parliament. Having failed to put this option on the ballot, Mr Salmond will paint a vote for independence as the last hope for a generation of empowering Edinburgh vis a vis London. If the unionists really are hard-headed, they will resist the complacency being fostered by the opinion polls.