Could that be a Willow Warbler? I say that purely because of the yellowing and the strong eye stripe
I would say a Sedge Warbler, especiaally considering the location.
It's a willow warbler or chiffchaff, you should have been able to i.d. it by the song in the last photo - if you can remember how it sounded. Chiffchaff gives very distinctive chiffchaff sound and willow warbler give a very distinctive descending scale. It isn't a juvenile either, just a bit scruffy
well, still NO positive ID then
Yes, Chiffchaff