In 1948 Vyvyan became a member of Benjamin Britten's English Opera Group (EOG), making her professional debut with the company as Jenny Diver in the première of Britten's version of John Gay's "The Beggar's Opera". She appeared in several more roles with the organisation over the next two years, including Nancy in "Albert Herring" and the Female Chorus in "The Rape of Lucretia". In 1951 she created the role of the Matron in the premiere of Brian Easdale's "The Sleeping Children" with the EOG in Cheltenham.