As a child, Clark sang in the chapel choir and showed a talent for mimicry, impersonating Vera Lynn, Carmen Miranda, and Sophie Tucker for her family and friends. Her father introduced her to theatre when he took her to see Flora Robson in a 1938 production of "Mary Stuart"; she later recalled that after the performance, "I made up my mind then and there I was going to be an actress. ... I wanted to be Ingrid Bergman more than anything else in the world." Her first public performances were as a singer, though, performing with an orchestra in the entrance hall of Bentall's Department Store in Kingston upon Thames for a tin of toffee and a gold wristwatch, in 1939.