@ greg stephens "I thought the poster was speaking for him/herself, and it surprised me"

He mentioned the "trad" possibility only after hearing Radcliffe or Maconie comment. On his own Sandy Denny blog the day before the radio broadcast he says of it: "It may be an original, but if so, with its cod mythology and sword-and-sorcery medievalism, it's not quite like anything else Sandy ever did" and he's just looking for any info he can find on it.
http://sandydenny.blogspot.com/2010/07/mystery-song.html