Again from 2 years ago, a small fly with large antennae: probably a male Rhaphium sp. (Diptera: Dolichopodidae). There are quite a few species of this genus on the UK checklist and in only a few do the males have these large antennae, one of these being Rhaphium calignosum. The females have normal-sized antennae.
A few days later I caught another one in mid-flight:
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2009-04-26 and 2009-05-01, respectively.