Yellow-legged Gull

Juvenile Yellow-legged Gull, Milton, 18th August 2009, © Dick Newell
Not infrequently, gull identification is not 100% certain, but there is enough here to be reasonably sure. In particular, the head and breast moult is well advanced and it has a few 2nd generation scapulars, as well as a new tertial. Other contenders would not look like this yet (RGN).