The Centrica-owned company called a review of its entire media business last month.
Aegis Media's Carat has held the account since 2002, after winning a consolidating review against Zenith¬Optimedia and OMD.
Last year, British Gas hired Publicis Groupe's Starcom MediaVest Group to handle the media planning and buying for its Business Services division, without a pitch.
The agency handled media for the British Gas Energy360 launch, which was created to help businesses improve the way that they use energy.
The media review will not affect the energy provider's relationships with its ad agencies, which include CHI & Partners, OgilvyOne, Ogilvy Interactive and Crayon.