Very common hoverfly on Creeping Buttercup at the moment. Legs all dark, but with yellow on the mid tarsal segments of the front legs.
No interactions present.
I think I can see the hairs, just above the hind knee in picture 1, is that right? And are the segments of the front tarsus not clear enough here to help?
latest pics and diptera videos
Yes, that is right on both counts. Cheilosia are really hard to ID from photos, as the details which tell each apart are very subtle. I think there is just about enough here to allow this one to go to albitarsis, but I am not expecting an agreement!
My Flickr photos...
Lat/Lng: 53.8833, -0.682
OS grid ref: SE867438