 aberdeen is a city with only one thing on its mind: oil. The roundabouts are pockmarked with signs for the "oil capital of Europe". The old-money granite houses in the West End have been turned into offices for the big energy firms, their former servants' quarters crammed with accountants and lawyers poring over contracts. and to get to the Patricia Cornwells at the airport's WH Smith you must first squeeze past shelves of books on all things crude, from Deepwater Horizon to a memoir called Don't Tell Mum I Work on the Rigs (subtitle: She Thinks I'm a Piano Player in a Whorehouse).  It's oil that gives aberdeen a special status in the litany of national grievances. Early in the North Sea bonanza, Scottish nationalists argued that the gusher of cash could be used in one of two ways: to prop up the British economy or to transform Scotland: "What do you want to be, rich Scots or poor Brits?" That question was settled decades ago - by a woman from Grantham.  "Margaret Thatcher destroyed British industry, and she paid off the unemployed with benefits using North Sea oil," says allan Macaskill, a petroleum engineer for more than 30 years. Macaskill is not a dispassionate observer - he joined the SNP when he was 18, and has a brother, Kenny, in the Scottish cabinet - but on this issue he seems to be voicing the local consensus.  Nationalist movements usually seek sustenance in stories of ancient wrongs and recent lost opportunities. Over the past few years, however, the SNP has had less recourse to What Might Have Beens and more scope to exercise greater power. Then came the elections of a fortnight ago, when the party won 53% of all seats at Holyrood, under an electoral system designed to prevent such majorities. "You were just watching the map of Scotland flip from orange and red to (SNP) yellow," says Karen, the PR manager showing me round the local harbour. "and there were all these people on telly chanting, 'Scotland! Scotland!'"  That night, the idea of an independent Scotland lurched from counterfactual fantasy to outside possibility. What that possibility amounts to might well be decided in aberdeen. The biggest, most seductive election promise  made by Salmond was that he would "re-industrialise Scotland", starting here. Those who say the oil is running out overstate rather than fabricate: more than half the local reserves have already been extracted and what's left will be harder and more expensive to pump out. In a manifesto festooned with pictures of windmills looming out of the water, the SNP laid out a plan to succeed North Sea oil with a giant renewable-energy industry.  Macaskill likes the idea so much he recently jumped tanker from the oil industry to set up an offshore-wind business. "You'll have cutting-edge technology developed right here, in aberdeen; you'll have wind turbines made in Glasgow and throughout the central belt. We'll have jobs again where our industries used to be." There is more to his enthusiasm than profit-seeking; this is the Scots' riposte to "the old Thatcherite idea of a post-industrial future".  For anyone bored with Ed Miliband and David Cameron arguing whether the spending cuts are "too far, too fast", the political debate north of the border can seem as starkly different as switching from black-and-white to colour.  In place of desiccated managerialism, Salmond and his finance minister John Swinney have come up with an economic strategy that serves also as a job-creation policy and a metaphor for national renewal. a re-energised Scotland: in the nation where it was once said that Clydeside built not only ships but men, such rhetoric resonates.  It's also pie in the sky, say critics. across town, a huddle of oil executives is having lunch with Brian Wilson, former energy minister under Tony Blair. "Nationalism is a fundamentalist belief, which uses economics as a rationale," he says, to nods around the table. "Scottish nationalism existed before the oil industry, but then oil became the answer. The SNP was around before renewables, but now alex Salmond talks about the North Sea becoming 'the Saudi arabia of wind'." My neighbour quotes some research showing that on present trends renewables will bring only 5,000 jobs to the north-east of Scotland: hardly an economic renaissance.  It's true that the clean-energy revolution is not yet visible to the naked eye. There's money for a European offshore wind centre, and talk of a green-manufacturing hub in the old oil platform-building site of Nigg on the Cromarty Firth - but the most noteworthy recent local development is Donald Trump's ?1bn golf course at Balmedie.  This vacuum neatly expresses the big economic problem for nationalists: in the 70s and 80s, their key task was to figure how best to spend the oil money; nowadays, the challenge is the more fundamental one of how to generate the cash for a post-North Sea future. In the 90s, nationalist pound notes were staked on hi-tech industry. But as foreign businesses bolted from Silicon Glen to asia, 20,000 people lost their jobs. after that came finance: Edinburgh was going to be "the Zurich of Scotland". Then came the collapse of Royal Bank of Scotland and Halifax Bank of Scotland. "It would be wrong to describe the SNP as making it up as they go along," says Brian ashcroft,  an economist at the University of Strathclyde. "But they are trying one thing after another."  Right now, though, the oilmen round this table are fuming over George Osborne's decision in March to jack up taxes on North Sea profits. "London behaves like an absentee landlord that just racks up tenants' rates," says one, to murmurs of agreement. That complaint is at the heart of the economic case for an independent Scotland. The SNP promises that self-determination will mean a smaller, closer government that tends to Scottish industry alone rather than trading it off against, say, the City.  How will that help? To find out, I speak to Graeme Bell, head of Green Ocean Energy and a poster boy for Salmond's renewables policy (not that he'll tell me which way he votes). We begin a game of Home Rule tennis, in which I serve the obvious question: what would an Edinburgh government give you that a London one couldn't?  "Regulatory clarity?" ah, but you can get muddled regulation out of Holyrood just as easily as Westminster.  "More funding to develop new technology?" There's plenty of cash in London and Dubai.  "We'd hope to have access to the Green Investment Bank." What, the institution brought to you by 11 Downing Street?  The point is almost mine, but then Bell lobs this in: "Sometimes you need an event to get people and things and an economy moving." and that event could be a severing of the union? "Possibly. I haven't seen a balance sheet that lays out the costs and benefits of independence, but I suspect that the result would be slightly positive."  If it's a cost-benefit analysis you're after you probably need an economist. Three hours south, in a glass-fronted cafe in the University of Edinburgh, I put Bell's challenge to a group of academics.  Simon Clark, head of the university's economics department, remarks that money would never be the deciding factor in any case for independence: "That would be like becoming a monarchist for economic reasons." But if Scotland were to cut itself loose now, what would its economy look like? Well, pretty similar to the rest of the UK.  Debates about the economics of independence often understate that it's London and the south-east - with its turbocapitalism and its chokehold on the Treasury - which is the regional anomaly. In Scotland, the public sector is a bit larger than the rest of the UK, providing employment for 25% of the workforce, above the national average of around 21%. Scotland's economy is more sluggish, growing by an average of 2% a year between 1997 and 2007, against 2.4% for the country as a whole. That may not sound much, but over the decades it adds up to a significant shortfall.  Notice what's missing from the economists' discussion: an argument about whether an independent nation could pay its way. That's partly because, so soon after Salmond's rout, the terms of separation are vague - how much of the oil revenues would go to Edinburgh; the public debt that Westminster would dump on Holyrood; even what currency it would adopt over the long run. But it's also because those Kelvin MacKenzie-isms about Scotland the Subsidy Junkie are - shock! - not wholly true.  The last set of figures from Holyrood statisticians show that for 2008-9, Scotland provided ?1.3bn more in revenue than was spent north of the border. at less than 1% of Scotland's GDP, that's not a huge surplus, and it does include a due share of North Sea revenues. Strip out crude and the deficit goes up sharply, to ?10.5bn (or 9% of GDP).  If those were your family's accounts you wouldn't want to be depending on one source of income that yo-yos so much (oil prices hit a record-high in 2008). But beware of double standards: hardly anyone put such objections to chancellor Gordon Brown during the bubble years.  The larger question that preoccupies the Edinburgh economists is what the business model for a stand-alone Scotland would look like. Unlike Graeme Bell, academic Stuart Sayer does not think the very fact of independence would change much: "It's like faith-healing. If you believe, wonderful things can happen - but I'd hate to rely on it as my sole treatment."  Follow Sayer's taxonomy and that makes Stephen Noon faith-healer-in-chief. He was in charge of putting together the SNP's manifesto for the last elections; and when we meet in in Edinburgh's George Street, he makes the case for nimble government: "Under our own government we could act now, rather than lobby the UK government for five years."  There would be extra money coming in too, he thinks, from revenues collected by Westminster but which belong to Scotland. "Because of Crown Estate, London collects hundreds of millions from renting out the UK seabed to offshore firms. That could be ours."  The argument that Edinburgh stands to rake in a tax bonanza is a familiar one to Michael Keating, a political scientist at the University of aberdeen. For him it's the flipside of a devolution system in which Westminster passes most of Scotland's budget to Holyrood, which then spends it.  No wonder Salmond now talks of an interim Basque option, based on the Spanish system. In this system, the majority of tax is raised locally and Edinburgh pays London for services such as defence and foreign embassies.  But as things stand, Edinburgh is about as fiscally autonomous as a teenager living off pocket money.  The result, says Keating, is a nationalist movement that hugs both the Swedish model of high public spending and the Irish example of low business taxes. "It's voodoo economics," he says.  It's also voodoo politics. This result is an SNP of both left and right, with frontbenchers well to the left of Labour and business supporters such as Sir George Mathewson, the former chairman of RBS. In the lobby of a hotel outside Holyrood, he tells me that "independence is the best way to deal with Scotland's dependency culture.  If the country stops taking money from London, then perhaps that will encourage our welfare claimants to stop taking benefits from the state."  Still, the left of the party would share Mathewson's view that separation would make for a more productive Scotland. In this argument, the country that brought you David Hume and adam Smith and the Scottish Enlightenment still has what urban theorists call the three Ts: "talent, technology, tolerance". Small and energetic, coffee-drinking and open-necked: the image projected is of Catalonia in woolly jumpers.  There is one problem wi 