Yellow and black striped hoverfly.
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Very hard from a photo to get to species on Syrphus. If a female has yellow hind femora, it is probably ribesii, but could be the very rare S. rectus, so you cannot be certain. If the femora are partly dark, it will be torvus or vitripennis, but then you need to see the presence of hairs on the eye, which is very difficult, and one or two other features. Most remain as just Syrphus, then!
My Flickr photos...
Thanks! I'll stick to Syrphus, then.
Lat/Lng: 51.36745, 0.00665
OS grid ref: TQ397650