Unknown gull at Chew Valley Lake, UK (1 Viewer)

We sighted a gull at Chew Valley Lake Saturday afternoon, 2/10/04, which we were unable to identify to our satisfaction. I have attached photos of it - it was very obliging and remained in view for a long time. Other birders suggested ring-billed but the plumage seemed very dark, and it didn't look like ones we have seen before (in Toronto). It appeared to be a very similar size to Lesser Black-Backed gulls which were present at the same time, but its bill didn't look right for a LBB, and much larger than the Black-Headed Gulls which it seemed to be hanging out with. We also considered Common Gull, again seemed to fit some characteristics but not all. Legs were white/grey to naked eye, Black pupil in eye had paler ring around it and then it was darker again round the outside of the eye. We would appreciate your input.
Jampots :h?:

This bird appears to me to be a sub adult Lesser Black-backed Gull. The mantle colour is far too dark for Ring-billed Gull. The bird also pocesses a red spot on the lower mandible, also illiminating the previously mentioned species. A good pointer for it being a sub adult is that the bird still seem to show pink legs (again, Ring-billed don't, they have yellow legs, but this varies somewhat). If you still are not sure I can go through various other pointers in depth, but hopefully this will suffice for now!

all the best

Hi jampots
I`m pretty sure that it's a 3rd W Graellsii.

The bill is of a sub-ad, The mantle colour is right for graellsii (if you look carefully, there does appear to be an hint of brown),The legs are pink(which is right for 3rdY).

regards Roger.