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:

A few pictures:

And a very short video here, you see the bird right at the end for about five seconds:

https://www.youtube.com/watch?v=91gv-piQfT0&feature=youtu.be

Much better sound here, again by A.Lewis:

http://www.youtube.com/watch?v=m6Gzb7ExThQ&feature=youtu.be

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.