He wrote The Complete Book of Thunderbirds, The Complete Gerry Anderson: The Authorised Episode Guide, and World of Thunderbirds: Exposing the Secrets of International Rescue (although for the latter book, he is not the sole author). Additionally Bentley wrote a number of episode guides for Thunderbirds: A Complete Guide to the Classic Series. He also contributed an interview with Crispin Merrell, plus a feature about how the adventures of International Rescue continued in books, records, and TV commercials during the 1960s, to said book. Finally for Thunderbirds: The Vault, Bentley answered many of Marcus Hearn's queries.
Other work includes The Complete Book of Captain Scarlet, The Complete Book of Gerry Anderson's UFO (in addition to the revised and expanded edition), and The Avengers on Location.