The five tests

Is it good for employment? What is the impact on our financial services industry? What will the effect be on investment Is there sufficient flexibility to cope with the change? Can convergence between the British and European currencies be sustained?

Both pro- and anti-euro Conservatives have condemned Labour's policy on the single currency as confusing.

They are pressing ministers to go to Parliament to clarify their policy on the euro in the wake of the latest furore.

Prime Minister Tony Blair, who was in Spain on Friday for an EU-Latin America summit, has yet to speak to Mr Byers since he suggested legislation for a euro referendum could go to Parliament in the autumn.

The comments have fuelled speculation that ministers are gearing up for a referendum next spring.

Former minister Peter Mandelson suggested on Friday that if a referendum was to take place next year, it was likely to follow the same timetable of the 1975 poll.

That vote - on whether to stay in the European common market - which was agreed in March and held in June of that year.

"If there is a referendum next year - and I think the economic jury is still out on where that is a possible - that is what I believe the timetable will be that the government follows," said Mr Mandelson.

'Whipped up story'

He told BBC Radio 4's Today programme he did not believe there would be legislation on a referendum before the government's five economic tests were reached.

Eurosceptics and journalists were "whipping" up the story, said the ex-minister, although he did admit that Mr Byers may have been indiscreet.

He later told BBC Radio Five Live: "Honestly for Stephen, he would be better for sticking to transport, local government and the regions and leave the euro to others."

Michael Heseltine: Number 10 is playing politics

In its rebuttal of the reports, Downing Street stressed there were no plans for legislation unless and until the Treasury's five economic tests were met.

Tory leader Iain Duncan Smith claimed the prime minister had sent his transport secretary to brief journalists that he would start the referendum process this autumn.

He said: "When that news broke the prime minister panicked and denied all knowledge.

'Sham tests'

"What a way to run a government. More spin becomes more chaos."

Shadow Chancellor Michael Howard described the five tests as a "sham".

"The only test the government is interested in is 'will they win a referendum?'" he told Today.

Byers: Under pressure again

The pro-euro former Deputy Prime Minister Lord Heseltine accused Downing Street of "playing politics".

Number 10's denial was "couched in exactly the same words that the prime minister used before the general election when he said there wasn't going to be an increase in National Insurance", he said.

Speaking on BBC One's Question Time, Lord Heseltine said Mr Blair would almost certainly have decided on a timetable for euro entry years ago.

He urged the prime minister to "get off the fence" and take a positive lead.

That attack was countered by Europe Minister Peter Hain, who said Downing Street had been clear on the issue.

'Delicious irony'

"It said you cannot have legislation considered until the economic assessment has been made and nobody knows whether it will be made before or after the Queen's Speech."

Mr Hain said it would be made before June next year.

Liberal Democrat foreign affairs spokesman Menzies Campbell said: "It would be a delicious irony if Mr Byers were finally to lose his job on account of his truthfulness rather than for having misled the House of Commons."

Mr Byers was reported to have said privately to journalists the legislation would be hurried through both the Lords and the Commons.

This would allow voters to have their say some time next year - with speculation mounting of a 1 May vote.

The "unveiling" of the timetable comes after Mr Blair made some of his most pro-euro comments yet during his interview for BBC 2's Newsnight this week.