Gunson joined the group 11 years ago and will assume her role on 1 March 2010.
Derrick has been managing director of AYMTM since selling his company, MTM, to Motivcom in 2007. Since then he has worked on the merger and integration with AY to form the current firm.
"John and I have been friends, competitors and colleagues for many years and when Motivcom acquired MTM in 2007 we agreed a vision for the newly formed AYMTM and a two-to-three year plan to cement the merger and grow the business," said AYMTM chairman Nigel Cooper.
"In the last two years AYMTM has made more than £1m of operating profit, has an enviable client list and an excellent team. I guess he feels it's mission accomplished and is now looking at what else he can do within Motivcom."
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