The possible early distribution of the Goidelic and Brythonic speaking peoples is an interesting subject. I have read that the earliest Irish writings have internal hints of a Brythonic substructure. Also interesting are the hybrid place-names in Eastern Scotland with the first part being Brythonic and the second part being Goidelic. Let's face it, we really don't know much about all that stuff.

Also extremely interesting is how the aboriginal British share certain genetic traits with Basques.