The wing marks on this individual seem quite smudged - is it Scathophaga furcata?
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It does not look like a Scathophaga to me.
My Flickr photos...
Thanks, Ophrys, Jeremy. It looks like there are only a few UK species. I gather Steven Falk has a key in the Dipterists' Digest 2005, Vol 12 - which I may purchase.
Lat/Lng: 50.6776, -1.5138
OS grid ref: SZ344865