Claire Epstein was born in London on September 18, 1911, to an upper-class Anglo-Jewish family. Her father, Mordecai Epstein (born Manchester, c. 1890–d. 1946), the son of parents who had migrated from Latvia, was editor of The Statesman’s Yearbook. In 1910 he married Olga, née Oppenheimer (b. Germany 1890?–d. 1971), whose parents had migrated from Germany when she was a child. Olga, a homemaker, was active in WIZO and also in saving Jews from Germany prior to and during World War II. In addition to Claire, they had two sons: Edward Nathaniel, born in 1915, who died in 1992, and (Sir) Anthony, born in 1919.