Dennis started to learn the piano. He also played bugle in the school cadet band at Richmond Hill Preparatory School. From there he was sent to St Paul’s School in Kensington where he sang in the choir and played piano solos at concerts. In 1936 he left school and got a scholarship to the Royal Academy of Music where he learned the horn with his father as well as the piano and, from 1938, the organ. He learned a lot from his organ teacher G.D.Cunningham who had taught his uncle Alfred the piano some 40 years before.