On 4 September 1939, the day after Britain had declared war on Germany, the BBC Proms opened with extracts from Richard Wagner’s works including The Mastersingers of Nuremberg, Götterdämmerung, Tristan and Isolde, Tannhäuser and Die Walküre. Later concerts that year included works by Bach, Beethoven, Brahms, Mendelssohn, Strauss and a lot of Wagner. The BBC may have been an instrument of Britain’s war effort but few of even the most patriotic Britons thought it immoral to play the works of the great German classical composers. The following year, the BBC Symphony Orchestra, which had relocated to Bristol, opened its 1940...