LONDON (AFP) - Only one in three Britons would vote to stay in the European Union in a referendum promised by Prime Minister David Cameron, according to a poll published in the Financial Times on Monday.

Fifty per cent of Britons would vote to leave the bloc, 33 per cent would vote to stay in, and 17 per cent would not vote, the survey by Harris Interactive for the newspaper found.

Mr Cameron said in a speech on Jan 23 that he wants to renegotiate Britain's relationship with the EU and then put the new terms to the British public in an in-out referendum by the end of 2017.

Of those Britons who said they would vote to leave the EU, 12 per cent said they would definitely change their minds if there was a successful renegotiation, while 47 per cent said they possibly would, but 41 per cent said it would make no difference.

Forty-five per cent of voters said Britain still benefitted from its EU membership, against 34 per cent who said it did not.

Just 31 per cent said Britain's economy would be weaker outside the EU, while 33 per cent said it would be stronger, and 37 per cent said it would be the same.

Harris Interactive polled 2,114 British adults between Jan 29 and Feb 6.

Polls in Britain have shown a growing opposition to EU membership in recent months.