There was another book published some time ago on the same subject by someone named Mike Brocken.
I read the pre-publication version put up on the Musical Traditions site and found it poorly researched - much of it coming from interviews carried out in bars after club sessions - I found it difficult to read because of the sound of axe-grinding it generated.
Came to the conclusion that 'someone should do this properly sometime'.
I wonder if anybody came across it and has an opinion on it.   
Jim Carroll