Cameron will be making his long-awaited speech on the United Kingdom's future relationship with Europe on Wednesday. It was postponed last week due to the hostage crisis in Algeria.
He will acknowledge that public disillusionment with the EU is "at an all-time high," using his 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.
The announcement, coming after months of build-up around the contents of Cameron's speech, could placate increasingly anti-Europe elements of the prime minister's party but further isolate Britain diplomatically and from trade partners.
Cameron will propose Wednesday that the 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 will say, according to excerpts of his speech released in advance. "It will be an in-out referendum."
The stated possibility of a referendum is expected to further rattle business leaders and 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.
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."
Cameron will say Wednesday that he envisions a "new" EU built on five principles: competitiveness; flexibility; power flowing back to, not just away from, member states; democratic accountability; and fairness.
While he will reiterate his view that Britain should stay in the EU, the prime minister will concede that "democratic consent for the EU in Britain is now wafer thin."
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 will caution against those seeking to hold 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 will lay out mostly hinges on a Conservative victory in the next general election. Still, 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, Cameron will say.
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.
Opposition Labour Party leader Ed Miliband fired a salvo ahead of the speech, saying it would define Cameron as a "weak prime minister, being driven by his party."
Cassandra Vinograd can be reached at http://twitter.com/CassVinograd