If a referendum on membership took place today, 43 per cent of Britons would opt to leave the bloc, while 40 per cent would choose to stay and 17 per cent are undecided about how they would vote. The results are based on a survey of 1,004 adults from across the country.
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Less than two months ago, a similar poll put the “yes” camp ahead with 54 per cent support, while 46 per cent were in favour of leaving.
Prime Minister David Cameron has promised to hold an in-out referendum on membership by the end of 2017, but first he intends to try and renegotiate the UK's position within the 28-member group.
Migrant crisis weighs on minds
The poll results show a tight link to the migrant crisis, with 64 per cent of respondents saying they think Cameron is right to refuse to sign up to the bloc's migrant sharing plan.
And if the crisis worsens, the proportion of voters wanting to leave is set to increase further. 22 per cent of “yes” camp voters said that if the problem escalates, they could change their minds about remaining in the bloc.