Alex Salmond wants to keep the pound as part of a sterling monetary union after independence - but this has been ruled out by all the main pro-union parties at Westminster.
The Scottish Government has “repeatedly refused” to set out the cost of a separate currency to Scottish firms - despite setting out the £500 million bill facing UK businesses in “transaction costs” from cross-border trade with Scotland.
The SNP leader came under pressure at First Ministers Questions today over the findings of an official Holyrood report setting out the full costs.
Labour leader Johann Lamont said: “Transaction costs for the rest of the UK - the so-called George tax - work out at £9 per head for people in England, Wales and Northern Ireland.
“But if the Scottish Government’s own figures are to be believed, the cost in Scotland would be £75 a head.”
For individuals businesses in Scotland, the estimated £400 million cost of transactions works out at about £1,229 per firm, according to Holyrood’s Financial Scrutiny Unit. This compares with £109 per firm south of the border.
“No wonder they wouldn’t answer the question,” Ms Lamont said today.
“Given this would be the consequence of his plan to break up the United Kingdom - why should Scottish business pay the `Alex Tax?’” Ms Lamont added.
Chancellor George Osborne, along with Labour and Liberal Democrats at Westminster, last week ruled out the prospect of Scotland sharing the pound after independence.
Alex Salmond has insisted this is a “bluff” and warned that Westminster would be saddled with all of the UK’s £1.6 trillion of national debt as a result, as well the transaction cost impact.
Mr Salmond told MSPs today: “Our proposal is to share the pound and not have the transaction costs.
“It’s her proposal - that is Ed Balls and George Osborne’s proposal - to try and force Scotland into a different currency and impose transaction costs on Scottish and English business.
“I don’t think English businesses will take kindly to being asked to pay the George or Johann tax.”