In "The Dream Of Macsen Wledig" the Welsh offer their own explanation of the origins of the Bretons. You can find that wonderful story in "The Mabinogion" and I reccomend it. The Mabinogion makes the Welsh and the Bretons kin.
What I know about the good people of Cornwall is that, they were the nicest people I met in England.
What I know about the Basques is what my sister, who visited the Payes Basque said, "Basque men are very good looking, and some gestures are universal."