I think its a 1 CY Lesser Black-backed Gull, because there are some hints that are better for this than for Herring:
-pattern of greater coverts
-small head with slender bill
-I can imagine seeing a dark head with the right dark area surrounding the eye and ear-coverts that is better for LBB
-the tertials have a irregular border to the dark centers. Thats within variation for LBB, they appear not clearly notched to me. I know a 100% ID-book LBB should have narrower pale edges to tertilas, but thats within variation.
-I find it hard to asses the exact darkness of this bird, so I wouldnt argue that this bird is to pale for a LBB.
But there are two caveats:
I am no Gull Expert and normally learn from others here (Thank you to all, so helpfull!), so I hope to be corrected and learn!
I know there is much individual variation in Herring Gull, I couldnt for example ID this bird: http://www.gull-research.org/hg/hg1cy/h131304aug.htm
it's all correct what you wrote, Alexander, but in many cases not as easy appliable due to huge variation. fwiw, the bird looks like a LBBG to me as well. extremely accentuated dark shinns on tarsus might be added to the traits alexander summed up.
Thanks to all...this is the only bird of the 3 that landed for me to photograph but they were very large and dwarfed every bird near. The top of the wings were dark and the the span looked in the region of 1.50 m.
Here are a few extra shots....The ducks in the foreground were much nearer so don't give a good perspective.