I've recently (last weekend) returned from a week on the Azores, and spent a fair amount of my time, as usual, looking at the gulls on Terceira and Sao Miguel.
One pale 2cy 'Yellow-legged Gull type' bird stood out amongst the dark atlantis - one from the mainland perhaps or are we not totally in tune with the variability of local Azorean birds? However, Lesser Black-backed Gull is a relatively common winterer on the islands and despite its sturdy structure, this must be a considered option.
A must for anyone interested in large white-headed gulls on the Atlantic Isles is http://peteralfrey.blogspot.com/, where Peter poses a number of unanswered questions...
I've also attached shots of a 3cy smithsonianus, identified earlier this winter, for interest's sake. Although it has 'the look' i.e. a nice 'glauc-type' bill as well as retention of feathering on the coverts (and in flight the rectrices appeared all dark), is it possible to identify an individual such as this beyond all reasonable doubt in the UK for instance?