Britain is coming under pressure from the European Commission to say when it will honour its 25-year-old promise to go fully metric, converting miles to kilometres and pints to litres.

Günter Verheugen, EU enterprise commissioner, says he wants clarity on the issue, claiming he is facing pressure from British pro-metric campaigners to act.

Mr Verheugen’s officials are said to be in “constant contact” with the government, trying to establish a firm date for a changeover.

“At the end of the day they will have to tell us how they want to play it,” said Mr Verheugen’s spokesman.

Britain committed to full metrication in 1979 but won a derogation allowing it to delay some of the measures, including the changing of road signs and the abolition of the pint of beer and the acre.

“The pro-metric lobby wants the UK to do this as soon as possible,” Mr Verheugen’s spokesman said, but acknowledged there were very strong voices on the other side of the argument. “We want to avoid this becoming another Euro-scare story.”

Labour party figures say privately they have no intention of scrapping miles and pints and that the Commission knows their position.

But the government is wary of definitively ruling out full metrication since that would breach its obligations to set a deadline for a switchover under EU law.

The Department of Trade and Industry said: “Discussions have been going on for some time but there aren’t any plans for a change in the foreseeable future.” The main pro-metrication group in Britain is the UK Metric Association, which counts Lord Howe, the former Conservative foreign secretary, among its patrons.

The UKMA says it is not “strongly lobbying” the European Commission to ensure that the government stands by its commitments to set a date for full metric conversion but says it is constantly campaigning for metrication to be completed.

Roz Denny, of the group, said it was unlikely to bring a legal action.

“We’d prefer to work on persuasion rather forcing people to do it.”

Pound (in weight) and pint labels were removed from pre-packed goods in 1995. And since 2000 it has been illegal to sell loose products by reference to pound, pint or gallon with the exception of draught beer.

Britain’s love of its imperial measurements appears to be deep-seated, in spite of the mathematical complexity of the system compared with the metric system.