Medium sized gull, mostly white with small dark marking on the head and blaxk tipped tail feathers. Wings light grey.
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The gull on the right hand post appears, in this photo, to be a common gull, the others are, as you rightly say black headed (non breeding plumage). In your description, you mention black tipped tail feathers. The black is in fact on the wing tips, the tail feathers in adult black headed and common gulls are white.
If you add an identification for common gull, I can agree that for you as well.
Most are Black-headed Gulls, but there is an adult Common Gull on the right-hand post.
Look at the Common Gull on the right post it has yellow/green legs and there are white spots on the black wing tips. The other gulls on the psots have red legs and totally black wing tips./ so they are Black-heade Gulls.
Lat/Lng: 52.0, -0.8
OS grid ref: SP8740