Small Gull with grey/brown head patch; others in main Dart Estuary had blacker colouring around their heads.
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Looks like an adult (going into winter plumage) to me. What made you think it was a juvenile?
Thanks for feedback - only that it just seemed to me (as a novice) to be early in the year for winter plumage, and there were juvenile Herring Gulls about - am happy to accept winter plumage though.
Lat/Lng: 50.3514, -3.5776
OS grid ref: SX878513