An independent Scotland would be richer per head than the rest of the UK if it kept the proceeds from North Sea oil and gas, but would face a crisis when that revenue started to run out, according to the Institute for Fiscal Studies .

The IFS said public spending per head was £1,200 higher in Scotland than in the rest of the UK, but oil and gas revenues would be more than enough to pay for this, provided that they were allocated to Scotland on a geographical basis, rather than shared out equally within the UK. As a result, taking into account North Sea oil, “GDP per head is somewhat higher in Scotland than in the UK as a whole”, the IFS said. “If UK debt were shared on a per capita basis, an independent Scotland might inherit a slightly smaller debt-to-GDP ratio than that faced by the UK.”

However, the IFS said oil and gas revenues were “very volatile” and this could pose problems for an independent Scotland.

In the mid-1980s, if oil and gas revenues had been allocated on a geographical basis, they would have accounted for nearly half of Scottish revenue. By 1991-92 they would have accounted for just 3% of Scottish revenue; in 2008-09, they were back up to 20%.

There would be a further problem when the oil and gas started to run out, the IFS said.

“Like the UK as a whole, and most other developed nations, an independent Scotland would face some tough long-term choices in the face of spending pressures created by demographic change,” it said.

“If, as is likely, oil and gas revenues fall over the long run, then the fiscal challenge facing Scotland will be greater than that facing the UK.”