Haygarth was a busy television actor beginning in the late sixties, with appearances on The Protectors, Last of the Summer Wine, and I, Claudius (with Derek Jacobi). In the 1978 NBC miniseries Holocaust, he played brutish SS sergeant Heinz Muller, and played regular comedy roles on the sitcoms Rosie (1978-1981) and Kinvig (1981, in the title role). Later appearances included multiple installments of both Sharpe and Hornblower and episodes of The Bill, Lovejoy, Inspector Morse, A Touch of Frost, Bramwell, and Charles Dickens' Bleak House (as Mr. Gridley).
Film roles include Renfield in the 1979 version of Dracula, "Ivan with the Tractor" in John Cleese's Clockwise, and the voice of Mr. Tweedy in the animated feature Chicken Run. Other movie credits include The Human Factor (with Richard Attenborough), Percy (with Elke Sommer), The Dressmaker (with Billie Whitelaw), The Bride, and The Trial (with Kyle MacLachlan). He was cast to type as Friar Tuck in the 1982 TV movie Ivanhoe (with James Mason).