A few days ago I came across this male Bibionid fly. This surprised me as I tend to associate the Bibionidae with spring and early summer. However two species do come out in the autumn: Bibio clavipes and Bibio lepidus. I think this one is Bibio clavipes (Diptera: Bibionidae) based on the shape of the stigma (the dark spot on the leading edge of the wing) and its position relative to the vein that runs to it (see here for details), but I could be wrong.
Photos taken in the Wilderness, Whiteknights Park, Reading University grounds, Reading, UK, on 2011-10-09.