Plummeting oil and gas revenues pushed Scotland further into the red last year.
Official figures showed the nation’s geographical share of taxes generated from the North Sea fell by more than 40% – from £10billion in 2011-12 to £5.58billion.
Pro-Union campaigners claimed the Government Expenditure and Revenue (Gers) data fatally undermined the economic case for independence.
They said it highlighted the folly of basing budgets on volatile oil prices.
They also claimed the government of an independent Scotland taking power this year would be forced to put up taxes and cut spending on schools and health to close the £4.5billion gap.
But SNP ministers said the fall in oil revenues was partly due to tax deductible investment of £14billion – which would increase future revenues – and the unplanned closure of the Elgin gas field.
First Minister Alex Salmond said: “North Sea revenues fell by 41.5% between 2011-12 and 2012-13.
“This, in part, was caused by unplanned disruption to production and record capital investment by the oil and gas industry, which has doubled since 2010. This will reduce tax receipts in the short term but maximise tax revenues in the future.”
However, the members of the “No” campaign said the reduction was part of an ongoing trend, with revenues expected to fall by at least 20% this year as well.
According to Gers, Scotland had a net fiscal deficit of 8.3% of GDP in 2012-13, compared to 7.3% for the UK as a whole. The gap signals a worsening of Scotland’s position. Last year, Scotland’s deficit was 5% of GDP and the UK’s 7.9%.
The “No” campaign accused the SNP of setting out unrealistic figures in the independence white paper, Scotland’s Future.
Head of the pro-Union campaign Better Together, former chancellor Alistair Darling, said: “If Scotland was independent today we would have no option but to cut spending on services like schools and hospitals or put up taxes – or probably both. Oil revenues are a major source of Scotland’s income, but are a relatively small part of the UK economy. The drop in oil revenue is so big that it is the equivalent of the entire budget for Scottish schools.”
Mr Salmond said it was misleading to look at just one year, and a five-year period was a better gauge of economic prospects.
“The figures show that tax revenues generated in 2012-13 were £800 higher per head in Scotland compared with the UK, meaning that now, for every one of the last 33 years, tax receipts have been higher in Scotland than the UK,” he said. “Over the past five years, Scotland’s public finances have been relatively healthier than the UK’s by a total of £8.3billion – the equivalent of nearly £1,600 per person.”
Chief Secretary to the Treasury Danny Alexander backed the claim that the SNP’s argument had been undermined by its own figures. “It shows that in 2012-13, the Scottish deficit per person was almost £500 worse than that of the UK,” he said.