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Looked at earlier postings to compare, Willow Warbler and Chiffchaff look similar except for the following distinct differences - Chiffchaff has darker legs, and has a clear eye-ring. I don't see these two marks, therefore seek a bird expert's help to confirm.
Can usually be detected from a willow warbler by its distinctive calls which give it its name.
The song gives it its name. The call is distinctive, but is a soft, monosyllabic 'hweet'.
This is a Chiffchaff. I got excited for a moment at what appeared to be two pale wingbars in the first picture, but I think it is just light and shadow playing tricks!
My Flickr photos...
Lat/Lng: 51.432633, -0.144377
OS grid ref: TQ290720