Iberian Chiffchaff at Strumpshaw

I met the two Brians and Adrian at the Fen this morning: the walk around and forty minute stake out from Fen Hide were very unproductive, probably because of the penetrating cold northerly wind: a few Marsh Harriers, Cetti's and the expected warblers were just about it. However, there was one highlight: as I  walked from reception to the junction of the three paths I heard what I am absolutely certain was an Iberian Chiffchaff calling. I'm familiar with the species and instantly recognised the strange mix of Chiffchaff and Wood Warbler notes. I spent ten minutes listening, but only managed glimpses. So: ears open!