Walton's house in London was destroyed by German bombing in May 1941, after which he spent much of his time at Alice Wimborne's family house at Ashby St Ledgers in the countryside of Northamptonshire in the middle of England. While there, Walton worked on projects that had been in his mind for some time. In 1939 he had been planning a substantial chamber work, a string quartet, but he set it aside while composing his wartime film scores. In early 1945 he turned again to the quartet. Walton was conscious that Britten, with "Les Illuminations" (1940), the "Sinfonia da Requiem" (1942), and "Peter Grimes" in 1945, had produced a series of substantial works, while Walton had produced no major composition since the Violin Concerto in 1939. Among English critics and audiences, the Violin Concerto was not at first rated one of Walton's finest works. Because Heifetz had bought the exclusive rights to play the concerto for two years, it was not heard in Britain until 1941. The London premiere, with a less famous soloist, and in the unflattering acoustics of the Royal Albert Hall, did not immediately reveal the work as a masterpiece. The String Quartet in A minor, premiered in May 1947, was Walton's most substantial work of the 1940s. Kennedy calls it one of his finest achievements and "a sure sign that he had thrown off the trammels of his cinema style and rediscovered his true voice."