Duncan worked as a labourer (in England and Germany) after leaving school, and subsequently as a project planner with a telecomms manufacturer (1978–87), and as a programmer for the Stock Exchange (1988–91).
After graduating from school, Duncan worked as a laborer in both England and Germany. He then transitioned to a role as a project planner at a telecommunications firm from 1978 to 1987, followed by a position as a programmer for the Stock Exchange from 1988 to 1991.