Thanks for that Bob. Looking at maps of tribal areas recently, I've seen that different branches of tribes seemed to be all over the place: off-hand I remember the Cornovii in Caithness as well as in the south-west. There's been a book recently about the origin of the Celts, making a similar point that the people we call Celts wouldn't know the term, using tribal terms themselves, and the term Celt has a Greek provenance.

One odd point I've noticed, both myself, and picked up from others, is that Scotland on the one hand, and England and Wales together on the other, with the dividing line being the Whin Sill/Hadrian's Wall, each have a marker at the geographical centre, predating the Roman invasion. Scotland has the Fortingall yew, south Britain Arbor Low. If this means anything at all, it might imply a two-fold division of the island of some antiquity.