Christy was talking about Martin Carthy singing the song, so it seemed odd when he then sang it himself. Could it be that the BBC didn't have the song in their archives? If so, that's a pretty sad indictment, as it's not exactly obscure: it not only appears on the Martin Carthy CD Rite of Passage but also on the Watersons' big box set, A Mighty River of Song.

I can't imagine any other reason that Christy would sing one of his own Desert Island Discs, particularly after referring to someone else's recording of the song...