Chiffchaff or Willow Warbler ?

Chiffchaff or Willow Warbler ?

Observation - Chiffchaff or Willow Warbler ?. Description: Seen in dune slack scrub area late September. Chiffchaff ? or Willow Warbler

Seen in dune slack scrub area late September. Chiffchaff ? or Willow Warbler