Query: What did David Atherton co-found?
Context: The same local musical tradition produced eminent figures such as Sir William Walton (1902–88), son of an Oldham choirmaster and music teacher, Sir Thomas Beecham (1879–1961), born in St. Helens, who began his career by conducting local orchestras and Alan Rawsthorne (1905–71) born in Haslingden. The conductor David Atherton, co-founder of the London Sinfonietta, was born in Blackpool in 1944. Lancashire also produced more populist figures, such as early musical theatre composer Leslie Stuart (1863–1928), born in Southport, who began his musical career as organist of Salford Cathedral.