First recorded by Ray Noble & His Orchestra (US #15 1940).
Other hit versions by Vera Lynn (1940), The Glenn Miller Orchestra (US #2 1940).
From the wiki: “‘A Nightingale Sang in Berkeley Square’ is a romantic British popular song written in 1939 with by Eric Maschwitz and Manning Sherwin, composed in the then-small French fishing village of Le Lavandou. The song had its first performance in the summer of 1939 in a local bar, where the melody was played on piano by Sherwin with the help of the resident saxophonist. Maschwitz sang the words while holding a glass of wine, but nobody seemed impressed.