UK EU Out campaign takes 4-5% point lead

The campaign for Britain to leave the European Union has taken a 4-5 percentage point lead before the June 23 referendum, according to online polls by ICM and YouGov.

The swing towards "Out" with less than three weeks to go comes as both sides step up their campaigning to try to win over the large number of still undecided voters with warnings over the economy and immigration.

The ICM poll of 1741 people taken June 3-5 showed 48 per cent would vote to leave, up from 47 per cent a week earlier, while 43 per cent would opt to stay, down 1 percentage point from a week earlier.

The YouGov poll of 3495 people on June 1-3 showed 45 per cent would opt to leave the EU, up from 40 per cent in a comparable poll a month earlier, while 41 per cent would opt to stay, down from 42 per cent.

The poll showed 11 per cent of voters were still undecided, down 2 percentage points from a month earlier.

Of the eight most recently published surveys, one opinion poll was tied, two showed In ahead and five have showed Out in the lead, including a TNS online poll published on Monday and two previous ICM polls published last Tuesday.

"There has been a couple of polls in a row all showing movement towards Leave - I suppose there might be finally some movement in the race," Anthony Wells, director of political research at YouGov, said.

"ICM's weekly tracker and indeed at least two other polls published in the last 24 hours, suggest a move to Leave might have occurred," Martin Boon, director of research at ICM Unlimited, said in a statement.

Sterling fell below $US1.44. The pound fell 0.9 per cent to $US1.4371, having traded at $US1.4441 before the latest ICM poll was published. It had hit a three-week low of $US1.4352 in early Asian trade.

Wells said the so-called "Purdah" period which has prevented civil servants from making interventions in the referendum campaign since May 27 may have given Out campaigners such as Boris Johnson the space to push their arguments on immigration.