He has a twin sister, Elaine Thompson. In the early sixties they formed a singing duo, Elaine and Derek, and had a few records released. They appeared together in the film, Gonks Go Beat (1964).
Derek Thompson met his wife, Dee Sadler, when she appeared as Maggie, a
cave explorer, in an episode of Casualty (1986) in which Derek plays Charlie
Fairhead. Charlie rescued Maggie when she was trapped underground after
suffering a fit.