By Guy Faulconbridge and Kate Holton
LONDON (Reuters) - Opponents of Britain's European Union membership have edged into the lead over the past two weeks, according to a YouGov poll which indicated President Barack Obama's intervention failed to swing support behind "In" vote in a June 23 referendum.
The online survey for The Times taken on April 25-26 showed support for the Out campaign had risen 3 percentage points to 42 percent since a similar survey on April 12-14, while support for the "In" campaign had risen 1 percentage point to 41 percent.
President Barack Obama on Friday warned Britain would be "in the back of the queue" for a trade deal with the United States if it dropped out of the EU, an unusually strong intervention into British politics that "In" campaigners welcomed.
"Some have portrayed Obama's intervention as backfiring - I wouldn't go that far but this poll does suggest that Obama hasn't given the remain team a boost at all," Anthony Wells, director of political research at YouGov, said by telephone.
"It hasn't been a game changer, it hasn't shifted opinion - it hasn't really made much difference at all," said Wells. "We have had a neck and neck for months now and nothing seems to be moving that."
Beneath the headline figures, the YouGov poll indicated the In campaign was ahead on the economic arguments after a series of warnings about the dangers of leaving from the British Treasury, the Bank of England and even the OECD chief who asked British people to reflect on their own nakedness.
While opinion polls, which failed to predict Prime Minister David Cameron's victory in Britain's 2015 national election, have cast the referendum as too close to call, betting odds have indicated a strong probability of a vote to remain.
Betfair odds on Thursday indicated a 71 percent probability of an In vote. After Obama's intervention, the implied probability of Britain voting to remain, moved over 10 percentage points to as high as 75 percent on Monday.
A British exit would unleash volatility in foreign currency, stock and bond markets, undermine post-World War Two European efforts toward integration and raise questions about the 21st Century fate of the world's fifth largest economy.
"UP IN THE AIR"
The YouGov poll, of 1,650 people and with a margin of error of about 2-3 percent, comes after three other polls taken during or after Obama's visit:
* ORB telephone poll, April 20-24: Out on 43 percent versus In on 51 percent, 6 percent don't know.
* ICM online poll, April 22-24: Out on 46 percent versus In on 44 percent, 10 percent don't know.
* Survation telephone poll, April 25-26: Out on 38 percent versus In on 45 percent, 17 percent undecided.
After Obama's warning and similar comments from German politicians this week, German Foreign Minister Frank-Walter Steinmeier cautioned on Thursday against piling pressure on British voters.
"I don't think we'd be well advised to issue threats from Europe," Steinmeier said in Berlin.
Martin Sorrell, CEO of the world's biggest advertising company, said that the referendum looked finely balanced and that some companies, which he did not name, were putting off investment ahead of the referendum.
"The whole situation is up in the air," Sorrell, the pro-EU chief executive of London-headquartered WPP (LON:WPP), told Reuters. Obama's intervention enthused younger voters who are more pro-European but traditionally less likely to vote, he added.
The YouGov poll also suggested a big boost for the UK Independence Party (UKIP), whose anti-EU leader Nigel Farage was trusted by 23 percent of people on Europe while Prime Minister David Cameron was trusted by just 20 percent.
Though the Out campaign was in the lead, 35 percent of voters said they trusted Obama on Europe.
"The British people like Obama but that is not enough to change their opinion," said Wells at YouGov, adding that it was unclear if Obama's comments would add to the overall perception that major leaders all wanted Britain to remain in the block.