CHI saw off competition from the incumbent, M&C Saatchi and WCRS to win the account. The four-way pitch, which was called in January, was handled by the Haystack Group.
The win means CHI has circumnavigated a three-way client conflict that arises from a move by British Gas into domestic telephony. CHI's other clients include BT and Carphone Warehouse, which has unveiled plans to move into fixed-line telephony.
However, BT is expected to continue using Abbott Mead Vickers BBDO on its fixed-line business, while Carphone Warehouse will appoint a second agency to its roster to handle its fixed-line venture.
The win will come as a huge setback to BMP, but the blow will be cushioned by new business from the travel operator TUI, H Samuel, Kwik-Fit and the Canadian Tourist Commission, all of which were awarded this year.
BMP won the account in 1991, following a consolidation that saw the incumbents Young & Rubicam and Ogilvy & Mather taken off the British Gas agency roster.
The first fruit of the BMP relationship was the "Don't you just love being in control" campaign, which featured celebrities such as Larry Hagman, Harry Enfield and Bob Hoskins, using their thumbs to produce animated gas flames.
The agency has since used Caroline Aherne's comic creation Mrs Merton to advertise the company's products and services.
More recently, BMP produced a campaign for British Gas Telecom, which featured people using telephones to perform tasks that normally require a naked flame, such as cooking bacon.
British Gas is the latest edition to a burgeoning client list at CHI. This year, the agency has won Expedia, The Spectator, BT and extra business from Britvic.
British Gas, which is owned by Centrica, is now also expected to review its direct marketing account. Its current DM roster includes the below-the-line agencies WWAV Rapp Collins and EHS Brann.
Last year, British Gas consolidated its media planning and buying into Carat, following a four-way pitch involving the fellow incumbent OMD UK, MindShare and Zenith Media.
Despite losing its monopoly, British Gas still has 12.8m of the country's 20m gas customers. Earlier this year it was criticised by the industry watchdog, Energywatch, over billing difficulties that affected thousands of its electricity customers.
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