His father Horace Sydney Cropper was the principal violinist of the Liverpool Philharmonic Orchestra.
After Holst, he studied viola with Lionel Tertis (1937–38) before becoming the principal violist of the Liverpool Philharmonic Orchestra in 1939.
[2] In May 1939, whilst a member of the Charles Taylor String Quartet, Cropper’s viola was stolen and a broadcast performance from Bluecoat Chambers in Liverpool had to be abandoned.
[3] He played Mozart's Sinfonia Concertante for Violin and Viola some ten times with the Liverpool Philharmonic and the B.B.C.
He played Harold in Italy on three occasions with the B.B.C.N.S.O and Don Quixote no less than seven times with such cellists as Thomas Igloi,[4] Maurice Gendron in 1964, Paul Tortelier in 1967, Mstislav Rostropovich c.1975 and Heinrich Schiff in 1976.