Solitary Herring Gull sized gull at Dinton Pastures, Berkshire. Strange marking on bill.
No interactions present.
From the brown markings on the wings you can see that this is not an adult bird. The amount of grey, adult feathers would make it a 4th calendar-year bird (what we used to call 3rd-winter). In this plumage a dark band on the bill is not unusual.
I would agree with Bob that this is a 4th calendar year Herring Gull (hatched in 2007), but (and this is splitting hairs!) would suggest that it is in 3rd summer plumage rather than 3rd winter - or at least is in transition between the two.
Most large gulls have dark streaking on the head in their winter plumage, this one has a white head so would appear to have at least started its partial 'spring' moult despite the early date.
I have explained aging by calendar year here(and corrected my aging of a bird in the observation);
Lat/Lng: 51.4, -0.9
OS grid ref: SU7872