On behalf of Emma who sent in an email:-
Yesterday I found a bird in our utility room. It was JUST like your photo of an Icterine Warbler, and, less so but a little like the juvenile willow warbler photograph, BUT as I put it outside it splayed its tail feathers which were a crisp white with black ends. It definitely had the eye stripe and its beak was as a warbler.
We are surrounded by arable land and have a reed bed. The farmer had been spraying pig slurry if that helps! We are in Worcestershire postcode B50 4PF. Would like to know what it was.
With thanks in anticipation