Whitethroat will have more of a browner back, Willow Warbler would have more yellow on the bird and the legs are too dark for Willow Warbler.
I would say Chiffchaff but the head doesn't look quite right to me, I would say... maybe a Garden Warbler, but the body and neck area doesn't look quite right for a Garden Warbler.
I'd say that is a Lesser Whitethroat.