Bob Copper did indeed collect some extraordinary stuff. I think that his talents as a collector were somewhat overshadowed by his participation in his remarkable family tradition.
My favourite among those recordings of his, that I have heard, has to be the Hampshire singer, Enos White singing 'George Collins' ('Voice of the People' vol. 3). To my knowledge this has been released commercially at least twice (it's also on the Caedmon/Topic set, 'Folk Songs of Britain') yet it seems curiously neglected and unremarked upon. It is very high up in my top ten of recorded performances of English trad. songs.
Also on the same list would be another of Mr Copper's collections: Ben Butcher (also of Hampshire) singing 'Cruel Lincoln' (a version of the ballad, 'Lamkin'). This latter recording is also on VotP vol. 3.