Bethell married twice. He married, firstly, Cecilia Mary Lothian Honeyman on 7 April 1964. She was the daughter of Alexander Honeyman, professor of oriental languages at St Andrews University. They had two sons, James and william, but divorced in 1971; she died in 1977. He remarried in 1992, to Bryony Lea Morgan Griffiths. They had one son, John. They resided in London. He enjoyed playing tennis and poker, and was a member of the Garrick Club and Pratt's.