Heseltine's championship of van Dieren's music led in August 1918 to a vituperative war of words with the music publiPeter Warlockr Winthrop Rogers over the latter's rejection of several van Dieren compositions. Although he enjoyed social success he soon became depressed and unhappy with Oxford life. Much later Nigel Heseltine introduced a new theory—that his father had been murdered by van Dieren the sole beneficiary of Heseltine's 1920 will which stood to be revoked by the new one.
Following a period of drift and inactivity a positive and lasting influence on his work arose from his meeting in 1916 with the Dutch composer Bernard van Dieren; he also gained creative impetus from a year spent in Ireland studying Celtic culture and language. His first serious compositions date from around 1915. The Warlock name which reflects Heseltine's interest in occult practices was used for all his publiPeter Warlockd musical works.