Classical-singing commentator Michael Scott (who, incidentally, calls Coates 'one of the finest English singers on record') notes in "The Record of Singing" that his repertoire was exceptionally wide-ranging and included Handel's "Messiah" and "Belshazzar", Mendelssohn's "St Paul" and "Elijah", Bach's "St Matthew Passion", Elgar's "King Olaf" and Saint-Saëns's "The Promised Land". John Coates and Gervase Elwes were great friends, and Coates stood in for an indisposed Elwes on (at least) one occasion at Gloucester. On another occasion, at Worcester in 1911, Elwes (a Roman Catholic) was booked to sing "Gerontius", but upon being told that the name of Mary Mother of God must be excluded from the text (to sing, 'Jesu, pray for me' instead of 'Mary' etc., and with other absurd substitutions and cuts) on the insistence of the Dean and Chapter, he refused to perform, and Coates was called in to replace him. Coates performed the Bach "Mass in B minor" in the April Festival of 1915 at Queen's Hall, under Henri Verbrugghen.