Fledgling bird for ID.
A lot of Stonechats in the area but also one or two warblers (not sure what type).
No interactions present.
Was just about to add 'Willow Warbler' but better coming from you.
Wondered about garden warbler but too pale?
Garden Warbler never shows any yellow, lacks a bold supercilium and is an altogether heavier warbler than this. The only confusion would be with Chiffchaff.
My Flickr photos...
Lat/Lng: 54.571, -6.079
OS grid ref: NW364271