I was in a quandary at Horton Bank CP. Many Herring Gulls in all age ranges were present alongside a big headed adult gull with a darker mantle and a longer bill than its neighbours. YLG immediately sprang to mind but on looking at the photos it has large white primary wing blobs.
Also a pr of Goesunder. Many small gull species, the Mute Swan Coots and Moorhens.
The place is like a swamp.
PS The photos of the queried gull were unfit for publication.