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Thank you for your prompt reply.

An Update of the 1998 Checklist of Diptera of the British Isles [updated 28 July 2021]:

Boreoclytocerus dalii (Eaton, 1893) *
Boreoclytocerus ocellaris (Meigen, 1804) **
Boreoclytocerus rivosus (Tonnoir, 1919) ***

*Not included in National Biodiversity Network (NBN)
** >250 accepted records in NBN
*** No records in NBN

So this individual is likely to be Clytocerus (Boreoclytocerus) ocellaris. What do you think?