"what the artists in folk clubs do with mick jaggers music turns it back into folk music."

Not sure I can agree with that Al, my view is that you could dance ballroom wearing morris kit, but it would not make it morris. An acoustic version of a pop or rock song does not become 'folk' just because it is performed in a folk club. I am, as you will have seen from previous posts, quite comfortable with a new song being 'folk', but on the basis that 'folk music' is the musical tradition of a country or area, then that new song must in my view, show a respect for, and an influence from that tradition.

For example, the Bad Shepherds performing punk songs in a folk 'style' and with folk instruments does not make those songs folk. I'm comfortable to say they are punk songs performed in a 'folk style', which I believe is the way Ade Edmondson describes them. Although something like 'up the Junction' perhaps could fit as a narrative ballad. (That's not to say by the way, that I don't like The Bad Shepherds, and I've been lucky enough to appear on the same bill on a couple of occasions and love what they do) 'Whisky in the Jar' on the other hand, remains a folk song even when rocked up by Thin Lizzy.

John