I had scanned the flock a couple of times and only found a couple of argentatus, when out of nowhere a Gull dropped right into view, and straight away it was obviously a Caspo. I quickly got many photos and ran over in my mind as many features as I could remember, and they all fitted.
This was the fourth or fifth day running of looking at a series of Gull flocks, so I spent two hours watching the bird, later being joined by Chris Glanfield who had pretty good views. The Spoonbill was also seen on the east side preening on the 2nd meander.
1st winter Caspian Gull in Cuckmere
Due to not being able to upload videos, here is a still taken
With the phone showing the white underwing coverts.
video of the 1st winter Caspian Gull - Cuckmere