The chancellor has attempted to ease the concerns of pro-euro campaigners troubled by his stance on the single currency.

Gordon Brown reaffirmed his European credentials on Sunday with a pledge that he has not ruled out joining the euro entirely.

Brown told GMTV's Sunday Programme that he was not opposed to the euro but would join when it was in the national interest to do so.

By June 7 he will have announced whether Britain's economy has met the five economic tests, with many experts believing it is likely to be a negative statement.

Having accepted this, pro-euro campaigners are pressing for the chancellor to revisit the issue before the next general election. Brown said he was not an ardent euro-sceptic and agreed that Britain's place was at the heart of Europe.

"I have always been pro-Europe. And by history, by geography, by economics we are very much part of Europe," he said.

"It would be entirely the wrong policy to take the Conservative Party's view on this issue. They would refuse to join the euro even if it was in the national economic interest to do so.

"That is to rule out the euro on grounds of dogma, something that is unacceptable to me," he said.

His comments followed a warning by the Britain in Europe campaign group that it could collapse if the government failed to set a deadline for joining the euro.

With polls continuing to suggest that a significant majority of voters are sceptical about joining the euro, the government would rely on the cross-party Britain in Europe group to play a key role in any referendum campaign.

But in an interview with the Guardian on Saturday its campaign director, Simon Buckby, said that "warm words" from the government would no longer be enough.

"How could I motivate my staff, invigorate senior businessmen, trade unionists and voluntary organisations if the government statement did not set out a clear route map to membership of the euro," he asked.

"Business wants to know it is the government's intention, not just their hope, that we will join the euro in this parliament.

"There can be no more wait and see - there has to be a game plan, with a transparent political strategy, to secure membership."

Buckby also warned that failure to set a timetable for euro membership would damage Britain's influence inside the EU.

He said that the prime minister would be seen as "weak and dithering" by other European leaders.