ED Balls has suggested he could resign as Chancellor in a future Labour government if it decided the UK would, after all, join a currency union with an independent Scotland.

The Shadow Chancellor also told MPs there was a stronger case to reject entering a currency union with a new Scottish state than there was when Britain had refused to join the euro.

And he warned that if a breakaway Scotland adopted its own currency, then, because it would be worth less than sterling, "you would very quickly get in your car and try and get your money out of Scotland; that's your bank run, that's your catastrophe".

Giving evidence to the Commons Scottish Affairs Committee, Mr Balls noted how in 2003 the Labour Government had rejected Britain joining the euro on the basis of Gordon Brown's famous five tests. Only one test, he said, on whether it was better for financial services could have been passed. "My conclusion now when you look at this decision and think about it in the same five tests framework...it wouldn't be four tests failed, it would be all five."

Mr Balls dismissed Alex Salmond's allegation that the rejection of a currency union by all three main UK parties was just bluff and bluster, branding the First Minister's claim "nonsense".

Asked if he would resign if a future Labour government reneged on its rejection and agreed to a currency union, he replied: "I could not imagine being part of the start of that negotiation, let alone the end."

Last night, a spokesman for John Swinney, the Scottish Finance Secretary, said Mr Balls' case had been undermined by his old boss Gordon Brown who had labelled the Westminster parties' approach to Scotland on currency as 'bullying'."