I took this on a hot afternoon late September 2008 at RSPB Dungeness. It's a big crop so I apologise for the fuzziness.
I've showed to a couple of experts and got two answers: Icterine and Chiff Chaff. Icterine rang a bell as there was mention of some sightings on the board in the shop - although I do appreciate that Chiff Chaff's are more common but would they still be here in late September (28th I believe)?
It looks a bit green but I'm pretty certain I got the white balance right (all the other pics from the same day are fine).