These were very common on Sallows within conifer plantation today. Very windy, though, so hard to photograph.
No interactions present.
Looks to me like twoi separate species - one is P.punctulatus but the one on the catkin is not - probably a Platycheirus in the peltatus group???
Revised thoughts - not even a Platycheirus - just would not give a name!!!
You may be right, Roger. There were so many punctulatus around that it was hard to pick anything else out! There was one male Melangyna quadrimaculata, though, which was good to find.
I shall remove that picture, in view of your doubt.
My Flickr photos...
Lat/Lng: 54.2877, -0.63
OS grid ref: SE892888