Yes, Bob and Ted, I agree about Spillett's Hayes biog. The Gelly I don't know - must have a look at that.
P.S. Checking out the Gelly has led me to Duncan Heining's Trad Dads, Dirty Boppers and Free Fusioneers: British Jazz, 1960-1975.
What I'm seeking, though, is not so much sociological analysis, but a factual account of the music and its players. The Hayes biog certainly gives that and Peter King's Flying High: A Jazz Life and Beyond would help, too.