A male soldier fly, probably Beris morrisii (Diptera: Stratiomyidae). Note the swollen black first tarsus on the hind legs. I thought this ought to be a useful clue as to the species and I initially found a good match with this photo of Beris schaposchnikowi (= B. schapschnikovi) at diptera.info, but felt a bit reluctant to assign my fly to such an obviously exotic eastern species just on general appearance. And it turned out I was right to be careful: I later came across these three threads on the French site Le Monde des Insects in which Stephane ('Chlorophane') indicates that B. schaposchnikowi is not found in Europe, but the very similar B. morrisii is.
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2010-05-06.