David Bell, the agency's chief executive, declined to put a value on the account but the loss is believed to cancel out the £10 million Reckitt Benckiser healthcare range assigned to the agency during the summer. Most activity on the brand is below the line.
The business is moving to the Midlands agency Rees Bradley Hepburn, where it complements the Land Rover dealership account that the agency already handles.
The realignment reflects the growing consolidation of the Land Rover and Jaguar operations since their acquisition by Ford.
Some staff are expected to follow the account but Bell warned that redundancies could not be ruled out. The agency has five "field" representatives and ten support staff on the business.
The appointment follows a pitch between the two incumbent agencies and McCann Central in Birmingham. The combined account includes all through-the-line work on the Jaguar and Land Rover dealerships brands.
Bell said: "The loss of Jaguar isn't too bad because of Reckitt Benckiser whose revenue will begin to kick in next year. It was a global consolidation that brought us that business - and it's global consolidation that has taken Jaguar away from us."
