Wasn't there myself obviously (I'm UK-based, Glastonbury) but a mate forwarded me a clip supposedly from that night and I've been trying to work out if it's the same event you're describing.
The footage shows three white lights in a fixed triangular formation moving at a steady pace with no rotation, no navigation strobes, and zero sound according to the person filming. What's catching my attention is the apparent size - if the witness estimate of altitude is anywhere near accurate the thing is enormous.
Has anyone managed to pull proper metadata from any of the recordings circulating? I do a lot of investigation work over here and the first thing I always check is whether the EXIF timestamp actually matches the claimed time, because that rules out a load of the obvious hoax scenarios straight away.
Also curious whether anyone tracked local air traffic on FlightRadar24 or similar for that window. That's usually my starting point before anything else.