Douglas started acting as a teenager, joining the Worthing, West Sussex repertory company, before making her West End theatre debut in 1958.

She made an uncredited appearance as an audience member in the 1958 film version of Six-Five Special.

She made her (non-speaking) film debut in 1959 in The Shakedown, and then appeared with Tommy Steele in It’s All Happening.

Douglas met fellow actor Kenneth More on the set of Some People in Bristol in 1962. After starting an affair, More divorced his wife, and the couple married on 17 March 1968. More died on 12 July 1982.

In 1988, she met Scottish playwright and director Bill Bryden at a dinner party arranged by mutual friend Marsha Hunt. They have lived together in west London since, and were married at City Hall, New York City in February 2009.

She is best remembered for her roles in several Carry On Films in the 1960s, including Carry On Cowboy (1965) as an all-singing and trigger-happy version of Annie Oakley. She then appeared in Carry On Screaming! (1966), Follow That Camel (1967) and Carry On Up the Khyber (1968). She has, by virtue of this association, appeared on many retrospective and spin-off programmes. Douglas made an appearance in North Wales in September 2005 to unveil a plaque dedicated to the filming of Carry On Up the Khyber, as part of the movie had been shot in Llanberis.

In October 2018 her debut novel, “Josephine: An Open Book” was published. It is fictional but partly based on her own experiences.