He was elected to the House of Commons at the 1983 general election with a majority of 14,205 votes for the new seat of Mid-Worcestershire. His political views were apparent from his maiden speech, in which he attacked the Sex Equality Bill, and he was an early member of the No Turning Back group. Following boundary changes to his constituency, he was not selected to fight the new seat with the same name, losing out to the sitting MP for Worcester, Peter Luff. Forth found a safe seat in the Outer London suburbs for Bromley and Chislehurst in the heart of the large London Borough of Bromley. He was elected to represent the seat in 1997, 2001 and 2005.