Christine Walker to step down from Walker Media

She formed the agency with Georgiadis, after she left her chief executive role at Zenith Media Services.

Walker's departure will trigger speculation about the future of the agency. M&C Saatchi owns 75% of Walker Media and chief executive David Kershaw recently aired his intention to buy the remaining 25% held by management.

At the end of June Walker will hand over the leadership of the agency to Georgiadis. She will also sell her remaining 14% stake in the agency to M&C Saatchi, which currently owns 75%.

Walker, who said she was leaving the agency "in great shape", intends to take some time out abroad before returning to the UK to pursue other interests. She will remain a shareholder in M&C Saatchi.

Georgiadis said: "I have learnt an enormous amount from Christine and over nearly a decade we have enjoyed a very fruitful partnership. I will, of course, miss her but I am also incredibly excited about the company's future and my role within it."

Walker Media was valued at £18m in 2004 when M&C Saatchi increased its stake from 46% to 75%. Walker netted £3m and was set to get another £3m after two years, and partner Georgiadias received £1.5m.

It is now the eighth largest media agency in the UK and has annual billings in excess of £300m.

Earlier in her career, Walker was part of the 1988 launch of Zenith Media Services out of the Saatchi & Saatchi media department under John Perriss. It was one of the defining moments in the evolution of media planning and buying out of a back office function of creative agencies.

Walker also worked at one of the prototype media agencies Ray Morgan & Partners, which was launched as a breakaway from creative shop Benton & Bowles in 1985.

Ray Morgan & Partners was independent from 1985 to 1988 when it became one of the founding agencies involved in the birth of Zenith Media Services.