[5] After World War II, Thomas' warm, lyrical contralto voice was heard in opera and concerts in England for almost three decades.
[6] In 1945, Thomas debuted with the Hallé Orchestra under conductor John Barbirolli, in Edward Elgar's Sea Pictures.
The same year, she sang the role of Konchakovna in Thomas Beecham's radio production of Alexander Borodin's Prince Igor.
She also sang Nancy in Albert Herring with Benjamin Britten's English Opera Group at the Cheltenham Festival in 1951.
[5] In 1953, she sang the roles of the Rhinemaiden Flosshilde in Das Rheingold and Götterdämmerung and the Valkyrie Rossweisse in Die Walküre in Rudolf Kempe's Covent Garden production of Wagner's ring cycle (also recording these roles) and Magdalena in Rafael Kubelík's Covent Garden production of Die Meistersinger von Nürnberg.
[5] In 1960, she created the role of Hermia in Benjamin Britten's opera, A Midsummer Night's Dream, which she performed at its premiere at Aldeburgh, then at the Holland festival and Covent Garden.
She was, perhaps, most admired for her performances as Angel in Elgar's The Dream of Gerontius, which she recorded in 1954 with Sargent, the Huddersfield Choral Society and the Royal Liverpool Philharmonic Orchestra.
[3] The Daily Telegraph wrote of this recording: "The luminous beauty of her tone, her perfect diction and the warmth and dignity with which she invested the music are a lesson for young singers.
"[4][7] With Sargent, she also recorded Felix Mendelssohn's Elijah[4] Messiah, Vaughan Williams's Serenade to Music,[5] Walton's Gloria[3] and a series of Gilbert and Sullivan mezzo-soprano roles: Pitti-Sing in The Mikado (1957); Tessa in The Gondoliers (1957); Phoebe in The Yeomen of the Guard (1958); Cousin Hebe in H.M.S.