The war of words between Westminster and Alex Salmond's government over whether an independent Scotland could use the pound escalated today as the Scottish First Minister defended his plans for a currency union.
Mr Salmond said forcing Scotland to use an alternative currency would cost businesses south of the border "many hundreds of millions of pounds".
He branded that the "George Tax" after UK Chancellor George Osborne, who last week ruled out a currency union.
In a speech in Edinburgh last week, the Tory Chancellor said: "If Scotland walks away from the UK, it walks away from the UK pound."
Today, Mr Salmond told business leaders in Aberdeen that "diktat" had "backfired badly" on those campaigning for Scotland to stay in the UK.
Mr Osborne in turn claimed Mr Salmond "now is a man without a plan", after the Chancellor and his Labour and Liberal Democrat counterparts Ed Balls and Danny Alexander all dismissed the idea of a currency union between Scotland and the rest of the UK.
Former chancellor Alistair Darling, the leader of the pro-UK Better Together campaign, said it was "now simple fact that Scotland cannot keep the pound if we leave the UK".
Mr Salmond said Mr Osborne had misrepresented the impact a currency union would have on the rest of the UK.
"The Chancellor downplayed the disadvantages to the rest of the UK from a sterling zone," Mr Salmond said.
"I am publishing today an estimate of the transaction costs he, the Chancellor, would potentially impose on businesses in the rest of the UK if he tried to force Scotland into a different currency.
"They run to many hundreds of millions of pounds.
"This charge - let's call it the George Tax - this would be impossible to sell to English business, to be charged by their own Chancellor for the privilege of exporting goods to Scotland."
The SNP leader, speaking in Aberdeen, said: "In short, what was presented by Mr Osborne was not an economic assessment but a campaign tactic."
He said that stance would backfire when Scots go to the ballot box to decide the country's future on September 18.
The First Minister claimed Mr Osborne's speech had been received "poorly" in Scotland.
"Phone-ins, newspaper polls taken after the Chancellor's statement indicated his diktat had backfired badly," he said.
"People do become sick and tired of the succession of day-tripping Conservative ministers flying up to Scotland to deliver lectures and then flying back to Westminster again."
He added: "No one with a semblance of understanding of Scottish history and indeed the Scottish character would have made a speech such as the Chancellor delivered last week. To be told that we have no rights to assets jointly built up is as insulting as it is demeaning.
"To be told there are things we can't do will certainly elicit a Scottish response that is as resolute as it is uncomfortable to the No campaign - it is 'yes, we can'.
"It is a sign of how out of touch and arrogant the Westminster establishment have become."
He insisted that the main UK parties would change tack on the issue of currency if Scots voted for independence.
"What is said by Westminster during the heat of a political campaign will differ greatly from the reality of life after the referendum," the First Minister said.
"In the event of a Yes vote, the campaigning will stop and the common sense agreements will start."