Yesterday there were quite a few of these orange flies in and around the trees near the lakes. They are the same as the orange fly that I wrote about back in May. Comparison of the wing patterns with those in images at diptera.info (in particular here, here, and here) confirms my earlier suspicion that they belong to genus Tetanocera (Diptera: Sciomyzidae), but I cannot narrow the classification down to the species. As I mentioned back in May, the larvae of Tetanocera prey upon fresh water snails.
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2009-07-19.