On the outbreak of war in 1939 Flemyng volunteered for the Royal Army Service Corps, and served with distinction, winning the Military Cross.

[2] In June 1931, at the age of 19, Flemyng made his stage debut, playing Kenneth Raglan in Patrick Hamilton's thriller Rope at the County Theatre, Truro.

[1] He made his first appearance in London at the Westminster Theatre in October 1931, walking on in The Anatomist, and during 1932 he toured with Violet Vanbrugh's company, playing Cyril Greenwood in After All.

The company was directed by William Armstrong, who became known for training future stars including Robert Donat, Rex Harrison, Michael Redgrave and Diana Wynyard.

[4] Flemyng was still under contract to the Liverpool company when Raymond Massey and Gladys Cooper offered him a major West End role in the comedy Worse Things Happen at Sea.

[8] He remained on Broadway to play Makepiece Lovell in No Time for Comedy; his notices were good: the stars of the production were Laurence Olivier and Katherine Cornell but the reviewer in The Stage said that Flemyng "comes close to walking away with the show".

[11] At the end of the war Flemyng's first appearance was as Lord Harpenden in Rattigan's While the Sun Shines in an ENSA tour that finished at the Théâtre Marigny, Paris.

[1] After returning to England, Flemyng appeared as Rowlie Bateson in Frank Vosper's People Like Us (July 1948), and Philotas in Rattigan's Adventure Story (June 1949).

According to Granger, Flemyng "revealed a new, unsuspected, strength" when he appeared with Alec Guinness in T. S. Eliot's blank verse play The Cocktail Party at the Edinburgh Festival and then London and New York, in 1949–50.

He toured southern Africa in Nancy Mitford's The Little Hut and Roger MacDougall's To Dorothy, A Son, and in London took over in the former from Robert Morley in the West End run.

[16] After a British tour in John Van Druten's comedy Bell, Book and Candle, Flemyng returned to Broadway in January 1957 to create the role of James Callifer in Graham Greene's The Potting Shed.

[1] Back in London, Flemyng played Richard Halton in On Approval (1966), Gregory Butler in Giles Cooper's Happy Family (1957), and Colonel Melkett in Black Comedy (1968).

[1] In 1980 Flemyng played Sorin in The Seagull with Barbara Jefford as Arkadina,[18] and the following year he co-starred in William Douglas-Home's The Kingfisher with Michael Denison and Dulcie Gray.

[2] Among his last stage performances was a return to The Chalk Garden in 1992, this time playing the Judge, to the Mrs St Maugham of Constance Cummings and the Miss Marigold of Jean Marsh.

The BBC relayed excerpts from the stage productions of The Guinea Pig in 1946 and Adventure Story in 1949, and he appeared with Gielgud in scenes from The Importance of Being Earnest in 1947.

Flemyng married Carmen Martha Sugars in November 1939;[4] by this time, she had switched from acting into theatrical décor, joining the design team Motley.