The blackness of this small fly caught my eye one day last summer. It is probably Rhinophora lepida (Diptera: Rhinophoridae). Rhinophorid flies are similiar to Tachinid flies and distinguishing these two families can be rather tricky. Their larvae are parasites of invertebrates, mainly woodlice.
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2009-07-16.