Derek served 30 years in the Civil Service, the latter 6 years as director general for Environmental Protection with the Department of the Environment until his retirement in 1996. He represented the United Kingdom and was chair of the Management Board of the European Environment Agency (1995-1999). He was on the board of the Environment Agency for England and Wales (1996-98) having been involved with its planning and creation.

He is a non-executive director of Severn Trent PLC, and chair of Jupiter Global Green Investment Trust. He is involved with several environmental organisations including the United Nations Environment and Development (UNED) Forum where he is chair and the Institute of International Environmental Development (IIED) where he is vice chair.