Crompton was brought up a Jehovah's Witness and served for a time in the 1960s as a 'special pioneer'. Having left the Witnesses in 1965 because of doctrinal disagreements he explored the Christian faith in various churches from the Free Evangelical to Unitarian. He joined the Methodist Church in 1981, trained for the ministry in Cambridge and was ordained in 1987. He has worked as a Methodist minister in Co. Durham, West Yorkshire and South Wales.