Tachinid fly Ramonda spathulata (Diptera: Tachinidae). The metallic greenish-grey body and the triangular shape formed by the wings at rest are characteristics of this species. Also note the big forward-pointing spines on the middle tibiae.
The individual in the above two photos was probably a female. In the following photo of a mating pair the male, though somewhat out of focus, seems to have a slightly narrower gap between the eyes on the top of the head:
Photos taken in Whiteknights Park, Reading University grounds, Reading, Uk, on 2012-04-06.