The latest work by Harker I can find reference to is his book on Robert Tressell and "The Ragged Trousered Philanthropists", 2003 (I haven't seen it but that would have been well worth doing). So I'd guess he is no longer working.

I don't have "Fakesong" but I do have Harker's earlier "One for the Money" which contains a chapter titled "Fakesong" which is a precis of the later book. As he says, he isn't attacking Sharp himself, but the followers who refused to examine where he was coming from. Which seems fair enough to me. The rest of the chapter is a history of the English second revival, and seems to me to be as good as you could get in the space, though as usual in Anglocentric accounts, Scotland hardly exists and continental Europe really, really doesn't exist.