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Euh, looking at the checklist: (http://www.dipter...CKLIST.pdf) That would be new for Great Britain. Checking Sander Bot & Frank van de Meutter Veldgids Zweefvliegen and my collection I would say I'm sure based on these photo's.
Dusted lunulae, shape of third antennal segment and arista and the black stripe on the face.
Very nice find!