An Iberian Chiffchaff came up on Birdguides so scooted over to Hayling Island for a look (and listen!). After a bit of tooing and froing, I eventually caught up with it and I thought it looked pretty good, right primary projection, mottling on the legs and correct colouration. The song also seemed good with a definite trill to it, sonogram by A.Lewis here including "wheep" notes:
And a very short video here, you see the bird right at the end for about five seconds:
Much better sound here, again by A.Lewis:
As ever though, we will have to wait and see with this one as the ID is not certain at this stage as far as I know.