Cuckoo Wasp

I was looking for gall flies on an aphid-infested burdock plant when this small metallic-green and orange wasp alighted among the aphids.  It stayed for a few seconds, just long enough for me to get a few blurry photos, before it flew off into the middle of a big patch of thistles.

It's a cuckoo wasp, possibly Hedychrydium roseum (Hymenoptera: Chrysididae), based mainly on the non-metallic look of the orange, but the above photo is not really clear enough for a proper identification.

Photo taken in The Wilderness, Whiteknights Park, Reading University grounds, Reading, on 2010-07-09.