Markings on abdomen and pinkish tinge on upper part not 'right' for the familiar H pendulus
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If you can't see the hind legs well, as here, females of Helophilus are harder to tell apart; and the upperpart pattern is not as clear cut as it is in males, so they do take careful checking. If it was hybridus, you'd expect more yellow down the side of the ocellar triangle, down the top side of the eyes. If it was trivittatus, you'd expect no black stripe from the antennae back to the ocellar triangle.
My Flickr photos...
Many thanks, Ian. It was the pinkish tinge on the abdomen which made me most doubtful, as it was rather reminiscent of H trivittatus.
Lat/Lng: 51.4, -0.03
OS grid ref: TQ371686
Photographed in an overgrown cemetery