Scotland would be forced to dump the pound for its own free-floating currency immediately after independence, the country's most eminent macroeconomist has warned as he denounced the "poor" plans produced by both sides of an SNP battle over the issue.

Professor Ronald MacDonald, research professor of macroeconomics and international finance at Glasgow University’s Adam Smith Business School, told the Telegraph a separate currency not linked to sterling would be needed to pay off the country's £16 billion balance of payments deficit.

He said the Scottish Government could not practically keep the pound on a temporary basis after independence, as proposed by Nicola Sturgeon, as it would lack the currency reserves required immediately after separation to keep clearing the balance of payments.

The latest official figures show a balance of payments deficit of 10 per cent of GDP. This means Scotland imports more goods, services and capital than it exports and a separate Scottish Government would be responsible for funding the gap.

Prof MacDonald similarly dismissed proposals by a group of SNP rebels to move more quickly to a currency pegged to sterling, saying: "It's very poorly thought out on either side of the divide."

The alternative blueprint would also require massive reserves to deal with the balance of payments, he said. Running down any available reserves "is not going to be a credible system," he added.