Charles Kennedy has challenged Tony Blair to set a date for holding a euro referendum next year.

The Liberal Democrat leader called on the prime minister to end speculation and announce when the vote will take place. Kennedy and suggested the anniversary of the historic poll that took Britain into what was the Common Market.

"It's time to concentrate minds. We should set a clear timetable for a referendum on the Euro next year. June 5 would be an obvious date - the exact anniversary as it happens of the pro-European victory in the 1975 referendum. That means a bill in this year's Queen's Speech to allow the vote to take place. It'll take two years from a successful yes vote before Britain can actually sign up to the Euro," he said.

In a speech to Britain in Europe on Monday, the most pro-European of the three main party leaders accused the government of dragging its feet on the issue.

"Put the referendum off any longer, and the next general election could take place before we're in. The last thing we need is the further confusion of the Tories campaigning in that election on a 'let's get out before it's too late' ticket," he said.

Kennedy called on the prime minister to have the courage of his convictions and fight for a "yes" vote.

"Up to now ministers, with one or two honourable exceptions, have been dragging not only their feet but every other part of their anatomies too. The prime minister's been particularly disappointing. I'd call on Tony Blair to have the courage of his convictions on Europe if I could really be sure that he had either courage or convictions on this issue," he said.

"What we need now is real commitment from the top. Just contrast the way in which another prime minister 30 years ago pursued the original goal of British membership of the Community. Ted Heath was single-minded, determined and visionary. If this prime minister won't claim his mantle, I shall be proud to do so."

Kennedy sees the issue as another opportunity to claim that his party is ahead of the debate.

He believes the euro issue going the same way as that of raising tax to pay for the NHS, one of the Liberal Democrat's election pledges which both the government and the Conservatives last week conceded may have to happen if the health service is to improve.

His gamble is that the vast majority of the country is not avidly euro-sceptic and once they have seen the benefits of entry or used the new currency while on holiday in Europe, they will back the idea of joining the single currency.

"These aren't people who are root and branch opponents of the euro and all its works. They're sceptics in the good sense of the word. Not blinkered bigots. People who like to ask questions and have them satisfactorily answered before they make their minds up. That's a perfectly reasonable position to take," he said.

He capitalised on the furore caused by Europe minister Peter Hain's interview with Le Figaro last week suggesting the government could give the green light to a referendum in the spring of 2003, with full euro-zone membership by late 2005.

But the Conservatives have also kept up the pressure against euro membership.

Shadow chancellor Michael Howard has written to Gordon Brown seeking clarification of whether entry in to the single currency would be an economic or political decision.

The letter followed remarks by foreign secretary Jack Straw that there may be "ambiguity" in the economic assessment of euro membership.

"So will the government be recommending euro membership if there is 'ambiguity' in the economic assessment, or not?

"It is perfectly clear that this complete change in position is designed to cover up the fact that entering the single currency will not be in Britain's interest," wrote Howard.