Alex Salmond has been urged to admit he misled voters during the 2014 independence referendum after the head of an SNP commission rejected his boast that oil revenues would have been a “bonus” rather than a necessity.

Andrew Wilson, a former SNP MSP and RBS economist, said that North Sea revenues had formed part of the “basis” of a separate Scotland’s finances rather than being an additional windfall as Mr Salmond repeatedly claimed.

He said that the commission, which has been charged by Nicola Sturgeon with building a credible economic case for independence, is assuming that the North Sea would produce zero tax revenues if she won a second referendum.

Unionist parties challenged the former First Minister to finally “own up” that he had misled Scots. Mr Salmond and Ms Sturgeon predicted a second oil boom and their White Paper forecast between £6.8 billion and £7.9 billion of revenues in the first year of independence.

The former First Minister claimed that North Sea revenues would be a “bonus” for a separate Scotland because there would be enough money from other sources to fund public spending. He said there would be additional sums that could be diverted into an oil fund.