Either that, or another wasp on steroids.
No interactions present.
This is a male - check out the very long antennae
In the inset photo it appears to be taking sap from some fresh damage to the bark. I'm not certain that it's the same individual - I thought the males died shortly after mating?
What you are seeing is ring-barking of young twigs to promote sap flow: commonly of Ash. Males are active for a few weeks each Autumn
I understand the behaviour now.
Lat/Lng: 52.4068, -0.236
OS grid ref: TL200802
Ancient ash-oak woodland