The launch of Britain in Europe in 1999 reflected cross-party support

One of the leading groups campaigning for British membership of the European single currency has said it could collapse if a referendum date is not set soon.

Simon Buckby, campaign director of Britain in Europe, said the organisation would suffer mass resignations if the vote on whether to join the euro was put back.

Chancellor Gordon Brown will publish the Treasury's assessment of the five economic tests in the coming weeks and is expected to say Britain is not ready.

Mr Buckby told BBC Radio 4's Today programme that Prime Minister Tony Blair will go down in history as a "ditherer", unless he calls the vote before the next election.

He said many businesses had made decisions based on Britain joining the euro and that failure to do so would mean "damage to our trade, damage to our investment, damage to our long-term prosperity".

'Shenanigans'

Mr Buckby said he hoped the chancellor would decide the economic tests had been passed.

If not, a referendum must be held later on in the current Parliament.

If the political direction is not clear, the prime minister will be seen by his European colleagues as another John Major or Harold Wilson, weak and dithering Simon Buckby Britain in Europe

"Lots of the independent commentators who have looked at the tests say that they should be passed," Mr Buckby said.

"If the government have allowed political shenanigans to get in the way and we don't get a positive assessment I think there will be a credibility gap."

Describing the threat to the future of his campaign group, Mr Buckby told the Guardian newspaper: "How could I motivate my staff, invigorate my senior businessmen, trade unionists and voluntary organisations without a believable route map to joining the euro soon?"

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

The campaign group has been pressing Mr Blair to keep open the option of holding a referendum in this parliament.

Public opinion

Its collapse would be an embarrassment for the prime minister, who has always maintained Britain's future ultimately lies within the single currency.

Britain in Europe was launched in 1999 amid huge fanfare and the rare sight of a platform shared by Mr Blair, Mr Brown, former Conservative deputy leader Michael Heseltine, former Chancellor Ken Clarke and Liberal Democrat leader Charles Kennedy.

We are the ones that will not take Britain into the euro Conservative leader Iain Duncan Smith Tories call for euro referendum

Mr Buckby warned Mr Blair's personal credibility among business leaders and politicians depended on firm action on this issue.

Opinion polls suggest there is not yet enough public support to win a referendum.

But pro-euro campaigners believe once a poll date is set, then the push to win support can begin in earnest.

On Saturday Conservative leader Iain Duncan Smith re-stated his opposition to the single currency and challenged the prime minister to hold a ballot without delay.