Link to a fascinating article by Scottish historian Tim Clarkson. Most students of Irish and Scottish history are very familiar with the Gall Ghaeil, but Tim Clarkson has proposed that there was also a Gall Bhreathanaigh. Gall Ghaeil means the foreign Gaels and Gall Bhreathanaigh means the foreign Britons, as in the Celtic people that lived in Scotland. This is linked to McCain history and our DNA results. When I have more time I will post an explanation. This article specifically about Clan Galbriath, but relative to the McCains.
The story here: The Viking Britons