Lester initially had small roles in several British television series, including The Human Jungle and Danger Man.

He also appeared in Spaceflight IC-1: An Adventure in Space (1965), played a small part as the second schoolboy in Fahrenheit 451 (1966) and had a larger role in Our Mother's House (1967).

In 1967, at the age of eight, Lester was cast in the title role in the film version of Lionel Bart's musical Oliver!

He played a disturbed child in the first regular episode of Then Came Bronson ("The Runner") and also guest starred on The Ghost & Mrs. Muir.

[6] Lester had leading roles in Eyewitness (1970), a British thriller with Susan George shot on Malta; The Boy Who Stole the Elephant (1970), a TV movie for Disney; and the horror film Whoever Slew Auntie Roo?

Tracy Hyde played the role of Melody in the film, which used music from the Bee Gees and Crosby, Stills, Nash & Young.

[10] Lester ended his film career playing the dual role as Edward VI of England and Tom Canty in the all-star film The Prince and the Pauper (US title: Crossed Swords, 1977) starring Raquel Welch, Charlton Heston, Rex Harrison, George C. Scott, and Oliver Reed, who had played Bill Sikes in Oliver!.