Small warbler difficult to see clearly due to moving around in foliage. Tried some shots with my camera and managed to get 3 images though not ideal. Main points are the very long & thin supercilium and the somewhat blotchy ear coverts, though not visible on photos, very brief binocular views showed a single rather thin wing bar. A nearby Yellow-browed Warbler was more successfully photographed! Have been in discussion about most likely species, but need some further thoughts before confirming. Photograph taken in Suffolk on 20th September.
Thanks Hazel, we've definitely ruled out chiffchaff due to the very long narrow supercilium, legs, general behaviour, call.