Sally Thomsett (born 3rd April 1950) is an English actress and was born in Sussex, England. She is best known for featuring in the film The Railway Children (1970), and for playing Jo in the TV sitcom, Man About the House (1973–76). She also appeared in the film, Straw Dogs (1971), where she played a young girl accidentally killed by the mentally handicapped character.
In 1970, Thomsett was cast as the 11-year-old Phyllis, despite the actress being 20 years old at the time, three years older than Jenny Agutter, who played her older sister, Bobbie. Her contract forbade her to reveal her true age during the making of the film, and she was not allowed to be seen smoking, drinking, driving her car, or in the company of her boyfriend during the shoot. She did have experience of playing girls, and the Edwardian smocks disguised her bust. Even the film crew were unaware of her age, and they gave her sweets while treating Agutter as nearly an adult. She did, however, make an appearance on BBC children's television shortly after, where the interviewer said, "I wouldn't dream of asking a lady her age, but you're obviously quite a bit older than the part you played in the film". She received a nomination for the BAFTA Film Award for Newcomer to Leading Film Roles.
For three years, in the 1970s, Thomsett dated fellow actor Richard O'Sullivan, at the time her co-star in Man About The House. She is married to Paul Agnew, a landscape gardener; they have one child, Charlotte Agnew.