As far as prog goes, this is where it's at. Experimental, RIO (rock in opposition), their first concert was opening for Pink Floyd, FRED FRITH (a genius), toured with Beefheart, made music that was challenging, avant-garde, often free-improv, jazzy, rock n' roll, always progressive, etc. etc.
I don't know how much more I can say, Henry Cow put out the most deliciously challenging blend of rock and jazz that my ears have heard... look it up.
Here's a sock:
