Heliomyzid imposter?
This fly (wing length 7 mm) came from mixed woodland in south Hampshire, at MV light on 14th August 2020. It keyed to Heleomyzidae, and had most of that Family’s characteristics – but not all. It has no F-bristles, and the frons is very narrow. There are two sizes of bristle along the costa, but the difference between the long and short ones isn’t great.