Nicola Sturgeon’s economic case for independence is “in tatters”, it has been claimed after official forecasts for North Sea tax revenues were cut again by more than a third.

The Office for Budget Responsibility (OBR) downgraded its forecast for offshore receipts by 37 per cent since last November’s Autumn Statement, from £7.3 billion over the next five years to £4.6 billion.

The most that oil and gas is projected to contribute to the public purse in any single tax year between 2017/18 and 2021/22 is £1 billion.

Labour and the Tories pointed out that the Scottish Government had Scottish revenues of up to £11.8billion in 2017-18 alone prior to the independence referendum, a figure they described as “a tissue of lies”.

Nicola Sturgeon, Alex Salmond and John Swinney have this week come under pressure to admit they were wrong during the 2014 independence campaign that oil would have been a “bonus” rather than a necessity.

The calls came after Andrew Wilson, who chairs the SNP’s growth commission, confirmed that North Sea taxes would have been needed to fund public spending and were not a windfall.

He said the group, which has been charged with building a credible economic case for independence, would now assume zero oil revenues. However, this leaves Scotland with a higher onshore deficit than even Greece's.