Latest News

The projected vote will be held only if his Conservative Party wins the election scheduled for 2015, he planned to say, and the ballot will take place in or before 2018.

Mr. Cameron had initially planned to deliver the address in the Netherlands on Friday but postponed it because of the hostage crisis in Algeria. The speech is a defining moment in Mr. Cameron's political career, reflecting a belief that by wresting some powers back from the E.U., he can win over the support of a grudging British public which has long been ambivalent – or actively hostile – toward the idea of European integration.

Speaking in London early on Wednesday, the excerpts said Mr. Cameron will say: "It is time for the British people to have their say. It is time to settle this European question in British politics."

"I say to the British people: this will be your decision. And when that choice comes, you will have an important choice to make about our country's destiny," according to the excerpts.

He ruled out an immediate ballot, saying that the turmoil within the 17-nation zone which uses the euro, of which Britain is not a member, meant that the broader European Union was heading for sweeping reforms.

A referendum before those changes are made, he said, would present an "entirely false choice."

In his speech, Mr. Cameron planned to say that he will ask for a mandate at the 2015 election for a Conservative government to negotiate a new relationship with the European Union.

"And when we have negotiated that new settlement, we will give the British people a referendum with a very simple in or out choice to stay in the E.U. on these new terms, or come out altogether. It will be an in-out referendum," he said.

Mr. Cameron added that he will complete the negotiation and hold this referendum within the first half of his next term, if he wins one, suggesting that the vote would take place in 2017.

Mr. Cameron had been under mounting pressure from his Conservative Party to make the announcement. The United States has been unusually public in its insistence that Britain, a close ally, stay in the union. Last week, a White House spokesman quoted President Obama as telling Mr. Cameron by telephone that "the United States values a strong U.K. in a strong European Union, which makes critical contributions to peace, prosperity and security in Europe and around the world."

Excerpts from the speech which were published on Friday quoted Mr. Cameron as saying that unless the European Union changed the way it is run, Britain would "drift toward the exit."

According to those excerpts, Mr. Cameron planned to note "a gap between the E.U. and its citizens which has grown dramatically in recent years and which represents a lack of democratic accountability and consent that is — yes — felt particularly acutely in Britain."

"If we don't address these challenges, the danger is that Europe will fail and the British people will drift toward the exit. I do not want that to happen. I want the European Union to be a success, and I want a relationship between Britain and the E.U. that keeps us in it."