One of the Eristalis sp hoverflies. I know it's difficult to go to sp, but...
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I can see why you went for an Eristalis, but it could not be Eristalis tenax, because that species has the hind tibiae wholly dark, and swollen in the middle with a fringe of hairs.
As Syrphus says, this is a very dark Myathropa, so the mistake was an easy one to make!
My Flickr photos...
Lat/Lng: 51.3, -0.1
OS grid ref: TQ3468