LONDON (Reuters) - The campaign for Britain to stay in the European Union has lost some of its lead over the rival "Out" camp ahead of Thursday's EU membership referendum, according to an opinion poll published on Tuesday.

The Survation poll, which was conducted for spread-betting firm IG, put support for "In" at 45 percent ahead of "Out" on 44 percent, IG said.

Survation's previous poll, for the Mail on Sunday newspaper and published late on Saturday, had shown "In" ahead of "Out" by 45-42 percent.

The new Survation poll was conducted by telephone on June 20, IG said.

(Reporting by David Milliken, writing by William Schomberg)