There was a great set of responses to Steve Arlow’s Essex gull here
When a first saw the images I said to Steve that it reminded me of some barabensis- particularly the Caspian Gull end (also called Steppe Gull- referring to large gulls breeding especially over central Asia and wintering roughly in the middle east to India especially dominating in the Gulf region). The rather compact appearance bright bare parts, dark iris, weakish bill pointed me in the direction. However to claim a barabensis this far west , for sure you would want darker saturated upperparts and black patterning in 7-8 primaries. So with that ‘feel’ to the bird, in the end I think I go for ID as small (female) Caspian Gull. Chris Gibbins is just back from an International Gull Conference in Zagreb, where they watched plenty of Caspian Gulls including some birds with bright bare parts in pre-breeding flush including bright yellow legs. He also thought the Essex bird best fit small Caspian, though seeing the full pattern on outer primaries would further help as others have said.
Had Steve been able to see the bird for more prolonged period, perhaps call and aspects of behaviour would have provided more clues.
So Caspian for me. Doesn’t mean I am right of course, but thanks for all those who wrestled with this bird and especially were bold enough to make a comment and have a go. Good learning!
Thanks again to Steve Arlow for some great images and a pioneering spirit