U.S. President Obama delivers a speech during his visit to Hanover Obama fails to swing Britain behind EU as 'Out' takes lead

Opponents of Britain's European Uni-on membership have edged into the lead over the past two weeks, according to a YouGov poll for The Times, indicating President Barack Obama may have failed to swing support behind "In" vote in a June 23 referendum.

The online survey taken on Monday and Tuesday 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.

U.S. 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 left the EU, an unusually strong intervention which "In" campaigners welcomed.

The proportion of those who said they did not know how they would vote fell 3 percentage points to 13 percent, according to the YouGov poll.

The YouGov poll also suggested a big boost for the UK Independence Party (UKIP), which has campaigned to leave the EU.

The poll showed UKIP leader Nigel Farage was now more trusted on Europe than Prime Minister David Cameron, with 23 percent saying they trusted Farage and just 20 percent saying they trusted Cameron.

Though the Out campaign was in the lead, 35 percent of voters said they trusted Obama on Europe while 32 percent said they trusted Boris Johnson, the leading member of the "Out" campaign.

(Writing by Guy Faulconbridge; additional reporting by Rama Venkat Raman in Bengaluru; Editing by Andy Bruce)