Phil - While Ruth is correct in saying that Folksong In England does not have "Blackleg Miner" in it's index the song is certainly in the book (pp 386/387 in the paperback edition)
I can only go back as far as 1966 when I first heard it sung at Birtley, by Pete Elliott - one of the first songs that I heard him perform, and I heard it from several North East club singers around the same time. Both Louis Killen and Bod Davenport had recorded it well before '66. Bert Lloyd had very strong connections with the North East and the Elliott family.
Charlotte- If you really want a millitant mining song couple "Blackleg Miner" with MacColl's "Daddy, What Did You Do In The Stike?"