Following an off-the-record briefing that a vote on euro membership is planned by the end of next year, Stephen Byers is today at the centre of a new row that combines Labour spinning and membership of the single currency.

During a lunch with journalists in Westminster, the transport secretary declared that while a Referendum Bill would not be included in the next Queen's Speech, journalists would then be briefed "the same day" that the bill would be forthcoming.

While the remarks were given on condition that he was named only as a "senior minister", Byers was promptly named by Labour MP and anti-euro campaigner Ian Davidson as the source.

The disclosure caused embarrassment for Number 10, which promptly disowned the claims.

"It is wrong to suggest there are any plans for legislation unless and until the five tests are met," said Downing Street.

Byers' remarks also annoyed the Treasury, which is reported to see the remarks as part of an attempt by pro-euro ministers to box in the chancellor.

Coming after Tony Blair's statement that it would be "crazy" to stand aside from Europe, the remarks are reported as more evidence of government determination to increase the momentum towards euro membership.

Conservative leader Iain Duncan Smith had earlier challenged the prime minister to hold the referendum.

"If he doesn't, he should shut up and get on with sorting out the health service and public transport and all the things that have gone wrong, the violent crime in the streets," he said.