In an interview with The Times on Saturday, Mr Cook promised to campaign for Britain to sign up to the single European currency when a referendum on the issue takes place.

Shadow Chancellor Francis Maude: "We have a much more international economy than the rest of Europe"

Shadow Chancellor Francis Maude called the inteview, which contrasts with recent cautious indications from Prime Minister Tony Blair and Chancellor Gordon Brown, a "rare blast of candour".

"If there is any difference of opinion in the Labour party over the euro, it is over how much of the truth about their policy they are prepared to tell the British people," he said.

"Robin Cook's message was loud and clear. Whatever the evidence, whatever our national interest and whatever the British people want, Labour are obsessed with abolishing the pound at the earliest opportunity."

Supports government policy

In the interview, Mr Cook warned of the dangers of staying out of a successful single currency.

Cook: Pledge to deliver pro-euro message

And he said he wanted to "open up" some of the arguments in favour of the euro.

He said: "I'm not going to give the Tory eurosceptics a free run in the press presenting one side of the picture.

"There are other aspects that need to be heard and I will continue to make sure they are heard."

He did not disagree with government policy on the single currency, which is to hold a referendum on joining when economic conditions are right for UK entry.

He said the government's existing policy had "done us well for the past two years and I think it will do us well for the next two years.

"That will provide the framework in which people like me can open up some of the arguments that need to be confronted when the referendum comes."

But head of research for the anti-euro Business For Sterling campaign Dominic Cummings said Mr Cook's words showed there was "confusion at the heart of government".

He said: "Robin Cook is talking about the risks of losing political influence.

"Unfortunately for Cook, the Department for Trade and Industry and the Treasury completely disagree with him. They say Britain will prosper in or out of the euro. This uncertainty is very bad for British business."