As for Polly On The Shore, it is of course a traditional lyric to which Peggy put a new tune for the Fairport version. JJs version uses a different melody. I'm not sure if he has restored a traditional melody to it but it stands in it's own right and it is only when I listen to the lyric that I remember that it is the same song.
I read that Jones had been listening to Alan Lomax prison song recordings, and chose to do an a percussive, a cappela approach to the backing for the lyric. I also think that he uses some different lyrics, which is something I enjoy in various renditions of traditional songs.