Gurney spent the last 15 years of his life in psychiatric hospitals, first for a short period at Barnwood House in Gloucester, and then at the City of London Mental Hospital, Dartford, where he was diagnosed as suffering from "delusional insanity (systematised)". Gurney wrote prolifically during the asylum years, producing some eight collections of verse. His output included two plays in Shakespearean style – "Gloucester Play (1926) and "The Tewkesbury Trial" (1926). During this time he appeared to believe himself to be Shakespeare in person. He continued also to compose music, but to a far lesser degree. An examination of his archive suggests that up to two-thirds of his musical output remains unpublished and unrecorded.