Dentsu Aegis’ subsidiary, Carat, has held the account since 2002, when it picked up the consolidated business after a pitch against ZenithOptimedia and OMD UK. OMD had previously handled the bulk of the business.
In 2010, Carat successfully defended the account after a final shoot-out against ZenithOptimedia and Mindshare.
Carat's sister agency, iProspect, handles digital.
It is thought that the home energy giant’s media account will attract interest from all six of the major ad agency holding groups.
ID Comms is understood to be advising on the pitch for British Gas, which is a top 20 advertiser in the UK, according to Nielsen.
British Gas' profits rose 31 per cent to £574 million last year.
But Centrica, the parent company of British Gas, reported a 12 per cent drop in profits and told investors last month it is "targeting £750 million per annum of like-for-like cost efficiencies from operating costs and controllable cost of goods, to be delivered over the next five years".
British Gas declined to comment.