I cant help. This bird lacks a clear white throat, whitish outer tail feathers, and although colours are difficult to judge due to warm light, this seems a Willow/Chiffchaff to me. More. I cant see contrasting tertials and I just can make out greeenish tones in the upperparts.
But which one? Although the bill seems large and pale (shouldnt even the Chiffies with the most extensive pale lower mandible still have a dark tip? Thats my experience), and the first colour impression says Willow, head pattern and PP (although difficult to judge, espacially on a bird with still growing feathers), I would set my money on a juvenile Chiffchaff.
Surely structure and head shape are wrong for chiffchaff or willow warbler? Looks good for whitethroat to me. The image is underexposed, so I tweaked it a bit (hope the OP doesn't mind), which I think helps to confirm common whitethroat. A young bird maybe?
The tertials are far too plain for a whitethroat, and it has a very prominent emargination on P3, which is not good for whitethroat, but much better for willow/chiff. The position of the p3 emargination on the wing and in relation to the other emarginations suggests this is a willow warbler, but I wouldn’t be sure.
Also - whitethroat would have paler legs than this
Willow warbler only gets its strong yellow tones after its post juv moult - so the yellow ones are first winters rather than juvs. While in juvenile plumage, willow warblers can be very dull underneath.