Hover fly feeding on a bramble flower.
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I can see now what you mean about Platycheirus. I've checked other photographs taken at the time, but they do not show any clearer characteristics. When you say female, would the male be noticeably narrower?
A male's abdomen would be narrower, if it were a Melanostoma. This is a female because the eyes are separated atop the head...in males, the eyes touch on top. The pointed tip to the abdomen is also a sign of a female.
My Flickr photos...
Lat/Lng: 51.796765702234, -3.6892175674438
OS grid ref: SN836122
Nant Llech (SSSI), the woods behind Wales Ape and Monkey Sanctuary, near Henrydd Falls.