He was Member of Parliament for Bolton North East from 1983 to 1997, originally as a Conservative before resigning to become an independent in February 1996 and then a Liberal Democrat in October 1996.
Thurnham became a design engineer at NEI Parsons in Newcastle until 1966, and then a director at British Steam Specialties until 1972.
He was noted for his very strong support for the Abortion Act 1967 and for embryo research, and was a founder member of the Progress campaign group which promotes IVF.
Thurnham was not interviewed, and Tim Collins - formerly an aide to John Major - was selected as the Conservative candidate instead.
He died of pancreatic cancer at home in Bentham, North Yorkshire on 10 May 2008, aged 69, the day after he married his second wife, Carole Emery.