At school, Van Ost became the youngest adult dancer at the London Palladium before moving into films and television at age 18. She appeared in four Carry On films - "Carry On Cabby" (1963), "Carry On Don't Lose Your Head" (1967), "Carry On Doctor" (also 1967) and "Carry On Again Doctor" (1969). Her other film roles included "The Beauty Jungle" (1964), "Mister Ten Per Cent" (1967), "Casino Royale" (1967), "Corruption" (1968), "The Smashing Bird I Used to Know" (1969), "Incense for the Damned" (1971), and the Hammer horror film "The Satanic Rites of Dracula" (1973). She appeared as the dim-witted Penny in an episode of "The Avengers" entitled "Dead Man's Treasure" (1967), and a year later was considered for the part of Diana Rigg's replacement as Steed's sidekick.