I think that the clips of Martin singing "William Taylor" plus his bit with the Watersons came from a BBC programme filmed in Nottingham, prod Phillip Donellan, called "The Other Music" c 1981
This would surely be worth showing again since apart from the aforementioned it also contained Ewan MacColl, Bert Lloyd, John Kirkpatrick, Jim Eldon, Roy Harris etc.etc.
Is this still available as it must be quite an valuable documentary especially to show to today's younger folkies.