A male Sphaerophoria scripta (Diptera: Syrphidae). There are several species of Sphaerophoria in the UK, but of them only S. scripta males are recognisable with any confidence from photos with their cylindrical abdomens which are clearly longer than their folded-back wings. Female S. scripta have more rounded, tapering abdomens but can only be safely distinguished from other Sphaerophororia females if they are caught in the act of mating with S. scripta males. The other Sphaerophoria species really require microscopic examination for their identification. In particular, the markings on the abdomen are not a good guide to the species.
Photos taken Whiteknights Park, Reading University grounds, Reading, UK, on 2011-04-27.