No interactions present.
Now I've found some Dolerus pictures this looks more like it
There aren't many with red 'knees' but there are some (D. puncticollis, D. gonager & poss. others). I think the thorax of D. gonager is shiny rather than hairy as here which matches D. puncticollis, but without a species key, I'd stick at genus too.
Yes, I did a bit of image browsing and found two or three different red-knee'd Dolerus of similar form so left it at that.
Is this an under-studied group given their size and numbers?
I might be wrong, but I suspect the problem is a lack of identification keys - I think they were covered in the 1950s RES handbooks, but these are not readily available and I imagine out of date - there is a 1981 update to part a which is available, but this doesn't cover the Tenthredinidae. There might be test keys out there somewhere...
Lat/Lng: 52.6, -1.2
OS grid ref: SK5701