I suppose your right with abberent herring, (maybe with abit of a leucisticism ( dont know how to spell it :P), But you know how much these gulls varyMB
Hmmmm couple of other people in the hide at the time got onto it as well and also agreed that it was just a Herring with increased white in the wing. If it had shown a few more thayers features we'd have been a lot more excited!
Why not Argentatus?
Un-streaked head, upper part colour same as the argenteus around it and still too much white in the wing, these drawings aren't the best. Definatley an interesting bird