King and Castle (1986)

Having hastily left the Met before his dubious activities finally caught up with him, ex-detective Ronald King has formed the Manor Debt Collection Agency with David Castle, a young, somewhat naive martial arts expert and part-time genealogist. Castle's skills come in handy in his new line of work, as do King's old police contacts, and in their dealings with a range of duplicitous, sometimes dangerous clients the chalk-and-cheese duo somehow manages to survive on the right side of the law.