He has also warned of the deep economic uncertainty that would face a newly-independent Scotland against a backdrop of continued global turmoil and questioned plans for its currency.
He said that if Scotland retained sterling as its currency it would face the same difficulties as the present eurozone, with a common currency whose central bank (the Bank of England) is based in a foreign country and without the ability to set its own interest rates and tax.
He said: "If you have a single currency area you come back to having an economic if not a political union. So, you go through all the trauma and expense of leaving the union, only to come back and discover that because you want to be part of this common currency you are back to where you were."
Which leaves the option of applying to join the Euro, hardly the most appetising prospect in the current climate, or launching a new Scottish currency.
He adds: "Frankly, given the financial turbulence we are likely to be seeing for some years to come, you would be a brave country indeed to say, 'here is our new currency - we are not actually sure how much it is going to be worth after the first day’s trading'."
Meanwhile, Scottish Secretary Michael Moore has asked for talks with Scotland's First Minister Alex Salmond on the independence referendum. Moore said the Government wants to provide Holyrood with "the legal powers for a fair and decisive referendum" to take place.
The Government said the first contact between the two administrations should be with the Scottish Secretary, who is leading its referendum consultation, and Alex Salmond.
Salmond confirmed he was ready to meet Prime Minister David Cameron "in Edinburgh, in London, or wherever" to discuss the way forward. The British Prime Minister had earlier offered to hold talks with the first minister over the referendum that could lead to a breakup of the United Kingdom.
Cameron’s offer followed a day of manoeuvring between the British government and Salmond's devolved Scottish administration as both sides competed for the high ground in an increasingly acrimonious debate over the future of the 300-year-old union between Scotland and England.
Salmond said this week he wanted to hold a referendum in late 2014 on breaking away from the rest of Britain, while Cameron has said it should be held sooner rather than later to dispel uncertainty he says is damaging the Scottish economy.
Cameron and all the main British parties want to keep the United Kingdom intact while Salmond's Scottish National Party (SNP) campaigns for Scottish independence.
Two opinion polls published today showed support for Scottish independence is stronger among English voters than it is among Scots.
The polls may reflect a view in some parts of Britain that Scotland gains financially from the current UK set-up, which gives its devolved parliament power over issues like health and education, funded by a grant from British government coffers.
The SNP says that view does not take account of North Sea oil revenues, which flow to the Treasury in London; an independent Scotland could definitely lay claim to a large part of those revenues. Both polls found Scottish opponents of independence leading supporters, although their lead in one poll was slim.
According to the poll, 43% of English voters are in favour of Scotland leaving the union, with 32% against. In Scotland, 40% backed independence, with 43% against.