I studied that case (or one just like it) in law school. As I recall (it has been a few years) an RAF Sergeant went into pub, chatted up a couple of RAF Arimen, and told them he and his wife were into kinky sex. Specifically she liked to act out rape fantasies and he liked to watch. If they cared to the Sergeant said (buying another round) they could accompany him home and have a go at his wife. She of course, he told them, would pretend she didn't know anything about it and beg them to stop...
I think the Sergeant was convicted, but the Law Lords over turned the airmen's conviction holding that given what they had been told they could have believed she was consenting and simply pretending to not consent.
Truth is stranger than fiction.
Yup -- I remember it, too --criminal law, mens rea chapter.