LONDON (REUTERS) - The number of Britons who back remaining in the European Union is level with those wanting to leave the bloc, with support for an exit growing, according to an opinion poll on Wednesday.

The ICM online poll found 42 per cent favoured ending Britain's membership of the EU with 41 per cent wanting to stay and the remainder unsure.

Excluding the "don't knows", the figures translated into a 50-50 per cent split, ICM said.

An ICM survey last week showed 52 per cent backed remaining in the bloc, with 48 per cent wanting to leave.