I found this large gull late morning at Mixenden and it conveniently landed on the buoy displacing an adult L B B Gull which was appreciably smaller. No scope!!! so dashed back for it and luckily the gull was still on the bouy when I got back. I managed to get a few digishots but it moved off, went high and drifted off >SE around 12.15.
First thing that struck me was its poise (very upright stance) and the shape of the bill leading straight to the sloping forehead, and particularly the long legs suggesting the possibility of Caspian Gull? It looks like a 1st winter bird? BUT I have not seen Caspian Gull before and would welcome comments. The other possibility is Gt B B Gull but I thought it looked too pale?