LONDON (Reuters) - The "remain" camp was ahead of "leave" by eight points in the latest ICM telephone poll ahead of Britain's EU referendum next month, but an online poll conducted by the same pollster at the same time found "leave" ahead by four points.
Britons will vote on June 23 on whether their country should remain in or leave the 28-member bloc, a decision with far-reaching consequences for trade, defense, migration, diplomacy and politics in Britain and far beyond.
Attempts to predict the outcome of the referendum have been complicated by a persistent divergence between telephone polls, which show "remain" ahead by a comfortable margin, and online polls, which suggest a tighter race that "leave" could win.
"Bemused? You have every right to be," said Martin Boon, director of ICM, in a commentary accompanying the latest set of polls.
"If you want to ask me, which is unlikely, the answer you’d get is 'I just don’t know,'" Boon wrote.
The polls were first published on the Guardian newspaper website on Monday.
The telephone poll found that support for remaining in the union stood at 47 percent, while "leave" was on 39 percent and 14 percent were undecided.
The online poll that "leave" was on 47 percent, "remain" on 43 percent and 10 percent were undecided.
Both polls were conducted on May 13-15. The telephone poll surveyed 1,002 people, while the online poll had 2,048 respondents. The questions were the same and the same weighting adjustments were applied to both sets of data, Boon wrote.
"I can see reasons why phone polls overstate 'remain' shares, and reasons why online polls overstate 'leave' shares. That inevitably leads to a conclusion that reality lies somewhere in the middle, but just hold that thought," he wrote.
"More aggressive weighting schemes ... employed on these very data sets - schemes intended to correct for observed (general election) vote intention skews the like of which have previously consumed us – are not reducing the gap on the EU referendum but increasing it."
In a similar set of polls released by ICM on April 19, the phone poll put "remain" on 48 percent, "leave" on 41 percent with 11 percent undecided.
The parallel online poll put "leave" on 44 percent, "remain" on 43 percent with 13 percent undecided.
The entire British polling industry failed to predict the Conservative Party's outright win in last year's general election.
Reporting by Estelle Shirbon; editing by Stephen Addison