Four days before the election, Robert Mundell, professor of economics at Columbia University, New York, not only backed fiscal autonomy for Scotland, which is SNP policy, but went further and said there was no reason why the country could not be successful under independence.

"Scotland is large enough to be a prosperous and independent country," he said, arguing that an independent Scotland as the EU's 26th member, would be the same size as Denmark and Finland and above eight other EU member states.

"As an independent member of the EU and the European Monetary Union, Scotland would be part of the largest common market in the world and share the second-most important currency in the world. There is no reason why a Scotland that was managed well could not flourish, taking advantage of her special geographical position, oil and sea resources."

Professor Mundell, 70, whose father was a Scottish soldier, won his Nobel prize in 1999 for his work on international monetary and fiscal policy and has been described as a major influence in the formation of the European single currency and the economic thinking of the Reagan White House.

He has served as an adviser to the UN, the World Bank, the International Monetary Fund, the US Federal Reserve Board, several governments in Latin America and Europe, and the European Commission.

Nationalists have argued that Scotland had the lowest growth in Europe under Labour at Holyrood. "Under independence, Scotland could not conceivably be worse off," said Andrew Wilson, shadow enterprise minister.

Professor Mundell argued that Scotland's political union with Britain had made sense when England was in its ascendancy and leading the empire. "The enduring legacy of the empire was to make the English language the most important in the world. But that era is now over," he said.

"The modern counterpart to the British Empire is the EU, which provides for 25 countries in Europe the political and economic umbrella that the British Empire provided earlier for countries like Scotland. I do not know whether Scotland needs a government in between its own parliament and what will one day probably become the federal capital of Europe in Brussels." He acknowledged the argument that Scotland's interest was recognised in Europe when Scotland was part of the UK presence in Brussels. "There will likely be both costs and benefits on either path, for example the potential benefit of having an independent voice in Europe versus the potential benefit of being part of a larger UK voice."

He added: "It would not be appropriate for an outsider to make a judgment as to whether the benefits of such a change are greater or less than the costs, and to whom."

He quoted Ireland as an example of a small EU independent state using tax incentives to be the fastest-growing economy in the Western world.

The Scottish Labour party said: "It is absolutely clear that Scotland benefits as part of the union from the lowest unemployment for a generation, the lowest mortgage rates for a generation and the lowest rate of inflation for a generation. While academics might find this an interesting debate the people of Scotland will have to choose this Thursday between the economic stability under Labour and constitutional upheaval under the SNP which would certainly reverse these low rates of unemployment, interest, and inflation."