Question concerning the Celts of the British Isles

[-Praetor-]

Wikipedia has some basic (and pretty interesting) stuff about it, here:

Pre-Indoeuropeans

An achaeologist here (Exeter) told me the Basques were the last vestiges of the people who first colonised Britain.

Well, the the most accepted and solid theory is that they are, in fact, vestigies of the first modern humans that colonised europe, well before the indoeuropeans. There are others, amongs them an alledged relation with the Iberians, so far discarded due to language dissimilarities. More about it, here:

Origin of Basques in Wikipedia

The conclusion we more or less agreed on was that there was a good chance the elite in Britain were Celts, while the peasents were "original" Britons.

And those britons being the subdued pre-inhabitants of the isles, which belonged to a pre-indoeuropean culture, similar to the basques. That might be the reason behind the genetic similarities between both human groups...