40mm long 2 pairs of wings front pair larger than hind. In flight slow with at least hind legs obvious and trailling.
No interactions present.
Definitely one of the two but either way a great spot! You may find this article interesting - http://www.radleyvillage.org.uk/news/news0083.htm
These large sawflies are tricky to identify, but the markings on the abdomen are an exact match for typical Cimbex connatus, so that gets my vote. Not something that's seen very often, a good record.
Entomologist and biological recorder
Lat/Lng: 52.9625, 0.6047
OS grid ref: TF750437