I think this might be a sawfly
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Sorry David posted at similar times you are pretty much there with it
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Plenty of Devils-bit around in bud, and the commoner of the two species I understand, so likely to be sericea but as you say cannot be sure. A male I think because of the depression on the abdomen, very interesting!
Lat/Lng: 51.329642, 0.192705
OS grid ref: TQ528612