@ Steve

Thanks for your explanation of how Harker set things back: I had guessed that this might be what you meant. Ironic, since, as Harker shows, people had been having similar thoughts for a long time!

I have found and been reading (tricky to get hold of but I managed it via googling etc) a review of two of Harker's works, including this one, by Vic Gammon.

It is 'Two for the Show': David Harker, Politics and Popular Song
Author(s): Vic Gammon. Source: History Workshop, No. 21 (Spring, 1986), pp. 147-156

Gammon says that Harker's book will win a place as a very important work of reference, while being quite critical of various aspects of Harker's 'preaching'.

Sharing the reference in case any other Mudcatter would like to see a reasoned response from a relatively 'left' position.