Alex Neil opposes the euro

But Mr Neil said: "There is no point in us jumping out of the British frying pan of sterling into a federal European fire of the euro."

He said that under Scottish devolution, the party should campaign for a "no" vote, and he questioned its very principle.

"With the euro the devil isn't just in the detail," he said.

"It's in the very principle of whether, either as an independent Scotland or as part of the UK, we should be part of a monetary union at all."

Mr Neil claimed that joining would limit the degree to which Scotland could be independent within Europe and he said: "How can we in the SNP argue for full fiscal freedom from London if we are then prepared to hand back fiscal powers to Brussels and Frankfurt?"

He added that if Scotland joined under devolution, it would have no influence in a set up in which the UK would be represented at Frankfurt by the Bank of England.

Recent policy review

Mr Neil said there was no evidence the euro would increase Scotland's level of trade or ability to export more.

He said: "Scotland's unique position as the largest oil producer in Europe means the ability to pursue an independent monetary policy is critically important."

But a party spokesman said the party had twice in recent years democratically decided its policy on the euro.

"We believe that the lower interest rates and stability offered by euro membership would benefit Scottish trade, tourism and inward investment," he said.

"The fact is that an independent Scotland in the euro would have 98% control over Scotland resources, compared to less than 10% as part of the UK."