In 1919 he was appointed Director of Music at Tonbridge School in Kent, returning to Oxford in 1924 to teach at Exeter College.
During this period he composed several choral-orchestral works including Forty Singing Seamen (1925), Master Mariners (1927) and The Ballad of Hampstead Heath (1927).
This prompted him to write his book Cobbers (1934) which the Australian Dictionary of Biography describes as "still the most perceptive and captivating characterization of Australia and its people ever written by a visitor".
He continued to compose and wrote several other books, including an autobiography, True Thomas (1936), before his death of a heart attack in 1950.
Before the marriage, on 7 June 1918 The London Gazette reported that St Osyth had been awarded an OBE for her work as "Hon Secretary, Essex Local War Pensions Committee".