His education began at the Imperial Service College where he first received organ lessons from Sir Walter Parratt,[2] and then at the Royal Academy of Music.
[3] From that year Middleton served as organist and conductor of the choir at Truro Cathedral (succeeding Mark James Monk), during which time he married Dorothy Mary Miller (on 7 January 1922).
[4] While at Truro he established himself as a prominent West Country organist and choral conductor, giving many opening recitals on newly installed or rebuilt organs, including St Martin's Church, Liskeard on 20 June 1923[5] and St Gwinear’s Church, Gwinear on 14 January 1925.
[8] After Edward Dent finished his tenure as professor of music at the University of Cambridge in 1941, no official successor was appointed for the rest of the war years, so Middleton took on the task of continuing Dent's reforms, designing the syllabus for the full tripos in music at Cambridge that came into effect in 1945.
[10] Middleton became highly regarded as an influential teacher, and his students at Cambridge included James Clifford Brown, Mary Berry, David Barlow, Mervyn Horder, Gerald Hocken Knight, Raymond Leppard, William Mann, Bernard Rose and Stephen Wilkinson.