Originally scheduled to mark Elizabeth II’s platinum jubilee year, English National Opera’s single performance of Britten’s Gloriana became instead a tribute to the late Queen’s memory, heightening, perhaps, the ambiguities of a work that holds an awkward place in the Britten canon. Commissioned for the coronation celebrations of 1953, it drew something of a blank at the time. Based on Lytton Strachey’s Elizabeth and Essex, the opera commemorates the start of the second Elizabethan age by chronicling the closing years of the first, and is essentially an ambivalent, darkly unsettling study of the loneliness of power and the sexual self-deceptions of age. The score is uneven and hampered by a dramatically clumsy first act, though later scenes contain some of Britten’s most resplendent music.