Marloes Mere - Iberian Chiffchaff?

A visiting birder heard 2 bursts of song from the Britton Hide today that he was pretty confident sounded like Iberian Chiffchaff (remember the odd singer I had there 2 weeks ago - see late May sightings). It wasn't seen and it was very windy, but certainly needs to be followed up. Before going, make sure you brush up on the classic IC song:

http://www.xeno-canto.org/europe/browse.php?query=Iberian+chiffchaff