With the warm weather in March I started to notice these small flies flying around the leaves of evergreen bushes on the edges of woodland. I recognised them as Chloropidae but from the photos it was difficult to tell which genus they belonged to.
On the 27th I took a specimen and examined it under my new microscope:
This shows the scutellum under x60 magnification. The shape of the scutellum and the arrangement of the two long hairs at the tip are characteristic of the genus Thaumatomyia (see here). In the similar-looking Chlorops genus the top of the scutellum is more rounded and the hairs at the tip are shorter and less parallel (see the 3rd picture here).
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2012-03-22 (first) and 2012-03-27 (second and third).