Cabinet minister Ken Clarke insisted today that Conservative MPs wanting Britain to leave the European Union were in a "tiny" minority and that David Cameron could not "conceivably" campaign for a No vote in his promised referendum.
The europhile Tory insisted that withdrawal would be "pretty catastrophic" and was only desired by about 30 of his Conservative colleagues.
He also warned of the dangers of holding a referendum, suggesting that parliament was better placed than the electorate to make such decisions.
The Prime Minister declared last week that he would renegotiate Britain's relationship with the EU and then put the result to a popular vote if Conservatives won the next general election in 2015.
Asked on BBC Radio 4's Today programme whether the Prime Minister could end up calling for a No vote, Mr Clarke said: "I don't think he could conceivably start urging people to vote No after all he said about his reasons for being members of the European Union.
"The whole policy is designed to stop this permanent battle about why we are in Europe and whether we should be in Europe and to improve our relationship with Europe and Europe itself."
Mr Clarke was dismissive of referendums, saying the public wanted one "on most things if you ask them".
He claimed that the Conservative Party was in fact "pro-European" and had been throughout his lifetime.
"There is a broad range of opinion within the party but the number of people that actually want to leave the EU is quite tiny. They get a disproportionate amount of attention," he said.
"My guess is there are about 30 Conservative MPs who want to leave and when we joined the European Community there were slightly more than that opposing Ted Heath's Bill."
He said eurosceptics wanted a referendum on the EU "because they know there is an overwhelming majority against them in parliament".
He went on: "Every politician of my generation thought that referenda were not as good as parliamentary democracy.
"When parliament votes all the members have continuing responsibility for the consequences of their vote and how things work out afterwards, and you can throw them out if things go wrong.
"But I'm resigned to fate, that is becoming a minority view in today's more activist world."
He said "it would be pretty catastrophic" if Britain voted No.
Mr Clarke, the Minister without Portfolio, joined former Labour cabinet minister Lord Mandelson last night to mount an impassioned defence of Britain's place in the EU.
Speaking at the launch of the cross-party Centre for British Influence campaign, Mr Clarke said it was essential to focus on the "positive things" Europe had to offer "and not just the things we are against".
Sharing a platform at the Westminster launch, Lord Mandelson accused opponents of putting out "lies and false propaganda", and called for an end to the "mindless, inward looking, soul-searching and navel-gazing" over Britain's place in the EU.
Liberal Democrat Cabinet minister Danny Alexander used the same event to dismiss suggestions the UK could rid itself of the bulk of its EU obligations as "nonsensical".
Mr Alexander, the Treasury Chief Secretary, said it was in Britain's national interest to "maximise our influence" in order to boost growth, trade and jobs.
"We cannot afford to give the impression that we are going to disengage," he said. "The idea that we should extract ourselves from the bulk of EU obligations is nonsensical."
The most outspoken comments came from Lord Mandelson, who bitterly denounced Eurosceptic critics of Britain's EU membership.
"For far too long, those who want to destroy Britain's interests and influence in Europe have been allowed to get away with murder with the lies and false propaganda they have poured out about the European Union and what it represents for our country. This cannot go unchallenged any more," he said.
"Instead of heading up a cul-de-sac of mindless, inward-looking, soul-searching and navel-gazing, we should be going out and spreading our influence and fighting for the agenda we think is good for Britain and for Europe as a whole."
Earlier, opening a Commons debate on Europe, Foreign Secretary William Hague vigorously defended Mr Cameron's referendum plan.
"It's our responsibility as one of the leading members of the EU to press for reforms that must happen if the EU is to succeed in this century; more competitiveness, flexibility, democratic accountability and fairness for countries both in the eurozone and outside it. All those will benefit the UK and the EU as a whole," he said.
"A one-size-fits-all approach for 27 member states is not what we have now, because it would be unworkable, and far from unravelling the EU, flexibility could bind us more closely together, because flexible, willing co-operation is a much stronger glue than compulsion from the centre."Suggest a correction