LONDON (Reuters) - Support for Britain to remain in the European Union stands at 45 percent while support for "Leave" is at 38 percent ahead of a referendum on EU membership on June 23, according to a Survation poll for online brokerage group IG published on Wednesday.

The poll of 1,003 people conducted by telephone on April 25-26 found that 17 percent of respondents were undecided.

It was the first in a series of polls IG said it would release between now and the referendum.

The probability of Remain winning the referendum stood at 73 percent on Wednesday according to bets on IG's platform, up from 64 percent this time last week. IG said U.S. President Barack Obama's intervention in favor of Remain last week was the main factor behind the increase.

However, in the poll, the Leave camp had improved its score by two percentage points since Survation's last poll on March 24, and by four points since the pollster's first telephone survey of the year on Feb. 20.

Throughout the build-up to the referendum, telephone polls have consistently shown Remain in the lead, while online polls have suggested the race was much tighter, with some finding Leave ahead.

(Reporting by Estelle Shirbon; editing by Stephen Addison)