I had a schedule to meet and had no time to get my camera out of the rucksack 😔. However I have spent some time on gull Id websites and conclude that this 2CY bird had the characteristics of a Caspian Gull. Not being more than 80% certain it won’t be recorded on BirdTrack.
A few LBBG present couple Herring many BHG & Common.
Ogden just had a dozen gulls a Buzzard & a Cormorant which flew off.