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I'm not great with gulls but is the wing colour not a little too dark for a common gull?
I'm no expert either but think Ophrys has it right. Dark wing (not Dark enough for Great Black-Back) and Yellow legs mark it as a Lesser Black-Back - there is size too but I think that can often be very tought when there is nothing to compare it with.
Feel free to look at my ongoing (hopefully improving) collection of pictures on Flickr:
Lat/Lng: 53.5583, -3.0687
OS grid ref: SD293073