Warbler-sized bird. Call is a single high pitched whistle.
No interactions present.
I'm glad I'm not the only one who has problems with this little devil. I had trouble with the bill length, but I think that's due to the moult. I suspect that the supercillium is also masked by the moult. Many thanks for your help.
I'm a bit confused by your attribution, ophrys, as a willow warbler in the heading and chiffchaff in your discussion.
So what is it? I don't think it's a reed warbler, it wasn't behaving that way - it was quite high in the tree, and not in the least shy or flighty.
I plumped for Willow.
My comment re Chiffchaff was the nearest I can come to humour, as usually, given a 50/50, I will opt the wrong way! Seriously, they are very difficult unless you can get a good picture of the primary projection on the wings. Unfortunately, no-one ever does! This one looks like a Chiffchaff in some photos, but a Willow for sure in the second picture, where the long, drawn out supercilium is clear.
My Flickr photos...
Ah! I see. Unfortunately the little chaps aren't always as helpful as they might be. By the time I located this one, and adjusted for bird against sky (so many silhouettes until I learned how to do that!), I only had a few seconds to photograph him (or her).
Nonetheless, I managed to get this image of the wing. Does it help?
Yes...that photo clinches the ID.
Counting the primary feathers from the outside (and including the first, very short feather, as No.1), the 2nd primary is equal in length to the 5th/6th. In Chiffchaff, that is usually equal to around the 7th/8th. The wing of Willow is longer and more pointed, in effect, befitting a long distance migrant.
Thanks for your help.
Lat/Lng: 52.08925, 0.05532
OS grid ref: TL409454
In tree near spring.