Nearly half of British voters could still be persuaded to change their minds before the EU referendum, according to a new poll out today.

Thirty-one per cent of voters polled by YouGov this summer said that they would "definitely" vote for the UK to stay in the EU, while 23 per cent said that they would "definitely" vote for a so-called Brexit.

Of the 46 who haven't made up their minds, 19 per cent said they were leaning toward voting to remain in the EU and 17 per cent said they were leaning toward voting to leave – but both groups said that they could be persuaded. The rest said they had "no strong preference" or "no idea".

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That is welcome news to both the Eurosceptic and Europhile camps who are gearing up to launch full-fledged "remain" and "leave" campaigns ahead of a referendum next year or the year after.

But YouGov warned that the playing field may not be as wide open as it seems.

By asking a series of detailed, policy-based questions, the pollsters found that voters leaning toward Brexit were mostly unconvinced by arguments to stay in the EU, while voters prone toward remaining were much more likely to be swayed by arguments to "leave".

In other words: the Europhiles may be looking at an uphill battle.

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Commenting on the findings, Anthony Wells, a director in YouGov's political and social research team, said the polling "shows potential for both sides", noting: "Those in favour of Britain’s membership of the EU currently have the lead and have a larger base of support. They also have the benefits of being the status quo option, meaning they have a head start in portraying themselves as the safe option and their opponents a leap in the dark.

But he added: "Obvious arguments in favour of EU membership poll badly when compared to some of the arguments against…The campaign to remain in the European Union need to find some arguments that are as effective as those of their opponents."