After failing to secure a short-service commission in the RAF, he completed his National Service in the RAF Regiment in northern Germany. Being, as he recalls, 'rebellious and stupid', he gave no thought on demob to further education, but took up an apprenticeship in a chemical company based in Castleford, near Leeds. I was guilty of making timber unrottable in a series of revolting houses in Newport which should have been allowed to rot very quickly'. At last, however, his intellect and senses were beginning to stir from their deep sleep. An interest in classical music had been sparked while in Germany by hearing Furtwangler conduct the Berlin Philharmonic orchestra in Kiel, an experience that affected him as strongly as any in his life.
Many artists love music.
Few know as much about it as Henderson. In Wales he began to read, to visit Cardiff's museums, and attend evening classes at its art school. Then crucially, he enrolled at the Barry Summer School in a small town west of Cardiff. There he encountered not just Terry Frost and Kenneth Martin but a great teacher and underrated artist, Harry Thubron. The course was called Colour, Form, Space, and it was a real eye and door opener.