Tullo Marshall Warren has worked on BA's direct marketing account for 18 years, while ZenithOptimedia has handled its media planning and buying since 2002.
Martin George, the BA commercial director, said: "We review our suppliers on an ongoing basis."
M&C Saatchi will make up to 15 staff redundant after losing the BA account.
However, it is not planning to shut any overseas offices.
BA will move to BBH on 14 November. The agency, which won the pitch with the line "upgrade to BA", is recruiting staff to run the business. Chris Harris, BBH's president of international operations, will run the account globally. Leo Burnett, which has a 49 per cent stake in BBH, will support the network in markets such as Australia and Africa.
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- Perspective, page 23.