Continental Form of Cormorant? (Phalacrocorax carbo)

Spotted on the rocks at Irvine Harbour today, this Cormorant which is unlike the local birds. A dip into an old bird guide threw up the suggestion that it is the Continental form of the Cormorant rather than the Atlantic form which is the one we usually see. White Breeding plumage just appearing on the nape of the neck. Anyone else seen this variation North of the Border?