Tredinnick contested the seat of Cardiff South and Penarth in 1983, coming second (with a 35.9% vote share) to James Callaghan, cutting the former Prime Minister's majority from 8,700 to 2,300 votes. He won Bosworth in Leicestershire in 1987. He became a Parliamentary Private Secretary, but was forced to resign in July 1994 after it emerged that he had abused parliamentary privilege by agreeing to accept payment of £1,000 from an undercover reporter to ask questions in Parliament about a non-existent drug. Part of the cash-for-questions affair, the MP was caught in an investigation by "The Sunday Times". In April 1995, he was suspended without salary from entering the House of Commons chamber for 20 sitting days.