seemed very small ,smaller than chiffchff ,was circling up and down aerial mast
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I think you are right, as the side-on picture seems to show a long primary projection. Difficult to agree, though, as detail is hard to see.
Be aware that Willow Warblers are bigger than Chiffchaffs. Especially, in terms of wing length, where the long-distance migrant Willows have a considerably longer wings than the more sedentary Chiffchaffs.
My Flickr photos...
Lat/Lng: 51.3819, -2.4123
OS grid ref: ST714648