With motorists facing record prices, Mr Cameron is under growing pressure to make good on his opposition promise to bring in a fuel duty stabiliser, which would reduce tax when basic fuel prices rose.

The idea was all but ruled out by the independent Office for Budget Responsibility but the Prime Minister last week hinted it was still on the agenda.

Now Scotland’s Alex Salmond has put his government on a war footing with Westminster by making a cut in petrol tax a key pledge in his bid for a second term in office.

Mr Salmond, who faces Scottish Parliamentary elections on May 5, told the Sunday Express he would be taking the battle to control the nation’s economy to Downing Street. His opening salvo was a promise to cut pump prices by 10p a litre if a campaign for Scotland’s own fuel price regulator was successful.

Mr Salmond said it was “extraordinary” that drivers in oil-rich Scotland were facing pump prices of between £1.20 and £1.30 a litre. “Before the election, George Osborne said he would have a fuel price regulator, which was originally an SNP proposal,” he said. “The idea being as oil prices increase you use that additional money, that unexpected bonus to offset against the fuel duty so you can provide some stability in fuel prices. You can take 10p off a litre. Oil revenues flowing into the London Exchequer will be £10billion this year, another £1billion from recent price increases, and yet we are paying the highest petrol prices in the world. It’s an unbelievable position. How on earth can you arrive at a situation where Europe’s leading oil producer, along with Norway, is in that position? No other country would stand for it.”