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I showed David your response and he replied ;-
"Ken Smith showed that the male of brevirostris usually has black stripes on the face in British material and that this does not occur in signatus, the only other spp that occurs here. There are consistent differences in the genitalia as well. It is true that males of this genus generally cannot be identified reliably, but until someone shows otherwise we can be reasonably certain that males with black facial stripes, like this specimen, are brevirostris".

So possibly a square go between you in a carpark of your choosing might be the only way to resolve the matter... My reply ;) [kidding] :)