Flagship plans to create a £30 billion oil fund after independence depend on being able to "spend the same money twice", peers heard yesterday.

Members of the House of Lords were told the Scottish Government would need much of the North Sea oil revenues to pay its bills.

Gavin McCrone, a former chief economist at the Scotland Office, suggested that the fund could only become a reality if the Scottish economy improved significantly. However, the expert said that independence could benefit Scotland economically, depending on the decisions of future Scottish governments.

Earlier this year Alex Salmond said that independence could allow Scotland to build an energy fund that would be worth £30bn within two decades.

The First Minister also said that that figure could have been £150bn if such a pot had been created in the 1970s.

Mr McCrone told peers he agreed in principle with the idea of an oil fund, similar to the one which exists in Norway.

"I agree with it, I wish to hell we had done it. If we had a fund like Norway our present [economic] situation would have been a great deal easier than it had been," he said.

He said the Scottish Government would struggle to set up such a fund at the moment. "They would have to get the economy working a hell of a lot better," he told members of the House of Lords Economic Affairs Committee, who are holding an inquiry into the potential impact of Scottish independence.

Mr McCrone suggested that the Scottish Government would need the oil revenues to meet public spending costs and would not have the surplus for a fund.

"Because you can't spend the same money twice", he added.