Another ichneumon wasp. I have no idea of the species nor genus. Out on the web, I was only able to find one image of anything similar (here), and there the front and middle femurs are much darker than on the above specimen. However, these little red-bodied ichneumons seem to fairly common in the long grass, this year at least (I can't speak for previous years). They seem very restless, flying this way and that, between the grass talks, pausing only occasionally, for no more than a few seconds at a time; frustratingly difficult to photograph.
Photo taken in Reading University grounds, Reading, UK, on 2009-06-16.