Clarke will take on additional London management and operational responsibilities, and continue to lead the new business function.
Meanwhile, Chris Stevenson has joined the agency to head up the London consumer team.
Stevenson also joins from Ketchum and replaces Richard Medley who has moved on to head up Publicis Consultants in London.
Stevenson has previously worked on FMCG brands such as Nike, Pepsi and Sony. He will handle business development in the UK and European consumer space.