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This looks similar to the hoverfly photo taken by 'Clouded Yellow' in the 'Wild About Britain' website where it is tentatively identified as H. trivittatus.
Your photo shows the entirely yellow face of trivittatus,
though the central reddish brown stripe on it is rare. Your photo also seems to show an all yellow mid tarsus which is another character of trivittatus (see British Hoverflies by Stubbs and Falk page 297).
Although the text in "Stubbs and Falk" suggest that a brown facial stripe is "rare" in this species, I find
I come across at least a slight hint of a stripe in this species fairly often. It is certainly not a strong black stripe, which would lead one to suspect one of the other Helophilus species.
In the field the general "jiz" is of a large, slender Helophilus with a lemon yellow body colour, not orange. The yellow is a little muted in the pictures, but I am wondering whether that may be an artifact produced by the camera as the yellow fly is sitting on a bright purple knapweed flower.
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Thanks again for your comments, it's good to have a bit of a discussion!
Lat/Lng: 52.1, -3.4
OS grid ref: SO0451