Prime Minister David Cameron said Wednesday he will offer British citizens a vote on whether to leave the European Union if his party wins the next election, a move which could trigger alarm among fellow member states.

He acknowledged that public disillusionment with the EU is "at an all-time high," using a long-awaited speech in central London to say that the terms of Britain's membership in the bloc should be revised and the country's citizens should have a say.

Cameron proposed Wednesday that his Conservative Party renegotiate the U.K.'s relationship with the European Union if it wins the next general election, expected in 2015.

"Once that new settlement has been negotiated, we will give the British people a referendum with a very simple in or out choice to stay in the EU on these new terms. Or come out altogether," Cameron said. "It will be an in-out referendum."

The stated possibility of a referendum is expected to frustrate other EU member states currently focused on stemming the euro zone debt crisis.

Already, speculation over a vote on leaving the EU has prompted a chorus of concern from around the world, stressing the importance of the U.K.'s presence in the bloc and warning about the economic consequences of a British exit.

U.S. favours 'strong U.K.' in bloc

Even the U.S., which normally stays out of disputes among EU states, waded into the debate.

The White House said last week President Barack Obama told Cameron in a phone call that "the United States values a strong U.K. in a strong European Union."

But Cameron stressed that his first priority is renegotiating the EU treaty — not leaving the bloc.

"I say to our European partners, frustrated as some of them no doubt are by Britain's attitude: work with us on this," he said.

Much of the criticism directed at Cameron has accused him of trying an "a la carte" approach to membership in the bloc and seeking to play by some but not all of its rules.

French Foreign Minister Laurent Fabius warned Wednesday that a British withdrawal from the EU would be dangerous for both the bloc and Britain.

"Say that Europe is a soccer club. You join this soccer club, but you can't say you want to play rugby," he told France-Info radio.

Membership of the EU has given the U.K. access to the massive joint European market as well as a say in how the region should govern itself and run its financial markets. The country has also benefited from EU funds to build infrastructure such as broadband networks.

'One size fits all' EU misguided: Cameron

Cameron insisted Wednesday that a "one size fits all" approach to the 27-nation EU is misguided. Britain, a fiercely independent island nation, has always had a fraught relationship with the bloc. It benefits from the single market but is among 10 of the EU countries not to use the euro.

"Let us not be misled by the fallacy that a deep and workable single market requires everything to be harmonized, to hanker after some unattainable and infinitely level playing field," he said. "Countries are different. They make different choices. We cannot harmonize everything."

Even as he raised the spectre of a referendum, Cameron reiterated his view that Britain should stay in the EU.

"I speak as British prime minister with a positive vision for the future of the European Union. A future in which Britain wants, and should want, to play a committed and active part," Cameron said. "There is no doubt that we are more powerful in Washington, in Beijing, in Delhi because we are a powerful player in the European Union."

But in order to stay, the bloc needs to change, Cameron said, as he laid out a vision of a "new" EU built on five principles: competitiveness; flexibility; power flowing back to, not just away from, member states; democratic accountability; and fairness.

Taking a direct swipe at those who have warned that raising the possibility of a referendum has created uncertainty for business, Cameron will say that questions about EU membership are "already there and won't go away."

But he cautioned against holding a vote immediately, saying it would be wrong to hold a referendum "before we have had a chance to put the relationship right" and before the euro zone emerges from crisis.

The timeline he laid out mostly hinges on a Conservative victory in the next general election. Still, Cameron said legislation will be drafted before 2015 so that if his party wins, it can be introduced and passed quickly enough to ensure a vote could be held "in the first half" of the next Parliament.

The Conservatives formed a coalition government with the Liberal Democrats after an inconclusive 2010 election. Pegging the possibility of a vote to an electoral win could be a gamble to appease increasingly vocal Conservative euroskeptics and stem the stream of voters who have jumped ship to the UK Independence Party, which advocates EU withdrawal.