Sumer Is Icumen In (The Pagan Sound Of British And Irish Folk 1966-75). A three disc compilation from Grapefruit that contains a few tracks I already have (Magnet's Corn Rigs is an example, Steeleye Span is well represented, there's some Fairport, Pentangle, Incredible String Band) and a whole bunch I don't. Well. Didn't. It's basically Acid Folk meets Folk Horror with that very British 70s sensibility that could be found underpinning many a pagan moot well into the late nineties. I ordered it from Red Cherry Records, as the MP3 version on Amazon doesn't have the full track listing -- clearly copyright issues prevented them releasing some of the tracks in digital format. I wouldn't have bothered with the MP3 version, although you can find it on Spotify or Amazon Unlimited if you have either of those.
Sam