But asked by journalists yesterday about the identities of the others, who include leading pro-European businessmen and women, he joked: "Some are uptight, middle-aged old farts."

Peter Bottomley, Conservative MP for Worthing West, said that if Mr Vaz "mis-spoke" he should correct his remarks and apologise immediately - the sooner the better.

Paul Keetch, a member of the Liberal Democrats' foreign affairs and defence team, also called on Mr Vaz to say he was sorry.

"Making stereotypical remarks about individuals is not helpful," he said.

"This minister would have readily condemned other people who made similar sweeping statements."

However, it was not Mr Vaz's only gaffe. The five-day roadshow will be travelling around the country on a Swedish-built Volvo bus called Eunice (EU-nice).

But according to a briefing note given out by the foreign office on the characteristics associated with particular names, a "weakness" of Eunice is "a tendency to make promises which you have difficulty keeping".

It adds: "You tend to be lavish in your nature and to spend your money freely."

The shadow foreign secretary, John Maples, said: "How very appropriate that Tony Blair's scrap-the-pound bus should be called Eunice, the very name of which stands for making promises that can't be kept, just like his government."

The roadshow will cover a dozen towns and cities in England, as well as going on a day trip to Paris, at a cost of £60,000, not including the hotel bills. Scotland and Wales will be included in tours to come.

Mr Vaz said: "This is a serious attempt to engage with the British people. Our message to them is that Britain's membership of the European Union is essential, rather than being an optional extra.

"What we are seeking to do is remind them of the benefits in cold economic terms: about their jobs, their prosperity, their way of life."

Eddie Izzard will join Mr Vaz on the Eurostar train to Paris at the end of the UK tour.

The aim is to meet 1,000 people a day. "If we do not positively engage [with people], we get isolated," Mr Vaz said.