It strikes me that the the Gulls in the picture might all belong to the same species and might all be of similar ages. They were standing beside the tidal Thames by Erith.
Looking at my book, 'Gulls of Europe, Asia & North America' (by Olsen and Larsson) it seems to me that they might be 2nd Winter Herring Gulls? First Winter birds would be darker? That being said, I could alternatively plump for First Winter, Lesser Black-Backed Gulls? I have boldly discarded Great Black-Backed Gull and Yellow-Legged Gulls!
I would be grateful if somebody could throw some light on this please?
A zillion thanks ~ Mike .....