Orchestration Revision
The orchestration of the concerto was revised in 1961 by Walton, with the premiere of the revised version being performed by John Coulling accompanied by the London Philharmonic Orchestra under Sir Malcolm Sargent on 18 January 1962.
The revised orchestration features 2 flutes (second doubling piccolo), oboe, cor anglais, 2 clarinets (second doubling bass clarinet), 2 bassoons, 4 horns, 2 trumpets, 3 trombones, timpani, harp and strings, compared to the original of 2 flutes, piccolo, 2 oboes, cor anglais, 2 clarinets, bass clarinet, 2 bassoons, contrabassoon, 4 horns, 3 trumpets, 3 trombones, tuba, timpani and strings.
Walton did not withdraw the earlier version, but did express a preference for the revised orchestration. Consequently, it is this version that is typically performed.
Read more about this topic: Viola Concerto (Walton)