The authors conclude that an independent Scotland would face a choice of reducing public expenditure, or raising interest rates and taxes, or a combination of all three.

The report - The Economics of Devolution and Independence - is written by Professor Sir Donald MacKay and Professor Peter Wood, who say they are politically independent. It was commissioned by stockbrokers Bell Lawrie White.

The research found that it was impossible to say what the long-term effect of independence would be.

But it concluded that there would be serious fiscal problems over the short-term, partly because Scotland's economy is very closely integrated with the rest of the UK.

Frank Malcolm, Corporate Finance Director of Bell Lawrie White, said: "The report clearly shows that the maintenance of current levels of spending in an independent Scotland would lead either to higher interest rates or heavier taxation or a combination of both.

Investment warning

"This would create an unfavourable environment for corporate Scotland compared to the rest of the UK.

"Inward investors and their managements would be less prepared to invest in Scotland and young talented managers would be less likely to stay. Furthermore, markets and businesses will not like even the uncertainty over the independence issue."

Sir Donald said public expenditure in Scotland was higher per capita than in the UK as a whole, and tax revenues per capita were lower.

He said: "As a result, an independent Scotland would inherit a 'negative dowry' in the form of the structural budget deficit."

The deficit would mean current public spending could not be maintained, necessitating spending cuts, higher interest rates and heavier taxation, or a combination of all three.

Union important

Sir Donald added that large revenues from oil and gas would not eliminate the deficit and would be subject to annual fluctuations.

"I would argue that the union in terms of access to markets has been very important for the development of Scotland's economy and remains so.

"But it is difficult to argue that Scotland would not be viable as an independent country.

"It is not clear that in the long term independence would be either seriously harmful or beneficial to living standards."

Labour's finance spokeswoman Wendy Alexander said: "This is another devastating blow to the SNP's plans to divorce Scotland from the rest of the UK and destroys their economic credibility.

SNP 'exposed'

"The SNP's claims that there is no black hole in their plans for divorce have been exposed as entirely false yet again. SNP economic policy has been holed below the waterline by Scotland's leading economic consultancy.

"It explains why they have been hiding their `Economic Strategy for Independence'. They must now immediately publish the full costs of their plans for divorce."