European Commission President Mr Romano Prodi warned Britain today it would lose control over its own economy if it remained outside the euro.
Challenging the widespread fear in Britain that signing up to the euro would mean a major surrender of sovereignty, Mr Prodi said the opposite was true. By staying outside the 12-nation euro-zone Britain would sacrifice its influence, he said.
"How can you control your economy, surrounded by the euro and not having your man in the European Central Bank?," Prodi asked reporters in London.
"The decisions are affecting you. You have to evaluate what is the biggest loss of sovereignty," he said, describing a decision to stay outside the euro as "a political choice which was not without consequence".
British Prime Minister Tony Blair says he favours joining the single currency in principle as long as key economic tests are met.
But opinion polls have shown a consistent two-thirds of people in Britain oppose entry.