One of the first hoverflies of this year for me: probably Eupeodes luniger (Diptera: Syrphidae), similar to Scaeva pyrastri but the yellow curved markings on its abdomen are yellow instead of white. (Actually, the curved markings on E. luniger seem to vary quite a lot in both curvature and thickness, see here and here.) The above specimen is probably a female, as is the following which I photographed a couple of weeks later:
Photos taken in the Wilderness, Whiteknights Park, Reading University grounds, Reading, UK, on 2010-04-20 (the male) and 2010-05-04 (the female).
A small chalcid wasp, probably not an Ormyrus sp. like the blue wasps I saw on oak leaves last year: the above wasp was on a thistle head (Cirsium sp), not oak, its abdomen was relatively smooth, not embossed, and its legs were mostly yellow, not black, so I feel fairly confident that this must be a different species.
Photo taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2010-06-29.