Ken Patterson, of Caedmon, has mentioned a recent programme on BBC Radio 4.
Presented by Paul Bayley, it's entitled The Strange Parallel World of Christian Pop and lasts just 30 minutes. Amazingly it manages to get through 30 minutes without referring to Cliff Richard or Graham Kendrick!
Starting with the CrossBeats in Liverpool, Paul gives an excellent tour of the way gospel musicians in the 60s and 70s pushed at the boundaries of music - and explains why so much has become so collectible recently. And yes there is reference to Parchment and the band's appeal to acid folk collectors.
You can find it here.