A British Union flag and a European Union flag hang from a building in central London.

The British campaign to stay in the European Union has taken a 15 percentage point lead over opponents of membership, according to a Survation opinion poll for the Mail on Sunday newspaper.

In the first opinion poll since Prime Minister David Cameron clinched a deal on Britain’s membership terms from other EU leaders, 48 percent of voters said they wanted to stay in the EU while 33 percent were in favor of leaving.

But 19 percent were undecided, the newspaper said. The poll showed that 35 percent of voters believe Cameron did well at the summit negotiations while 30 percent said he did badly, the newspaper said.

Cameron on Saturday called a June 23 referendum on membership of the European Union that could have far-reaching consequences for Britain’s unity and for the viability of the world’s biggest trading bloc.

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