The Britons didn't flee anywhere as the Romans let them keep their land, but Britannia stayed under the rule of Roman governors for over 300 years. It is true that they didn't pay much attention to north or Hadrian's wall (well, not for very long anyhow), but as the "empire" was all about wealth and commerce, it probably wasn't economically viable to finance a military presence there in the long term.
I would have thought the real mixing of the gene pool came under Anglo-Saxon rule.
Colchester was the Roman Capital of England,it was called Camulodunum.
As further research I did on that, I have to recant what I thought was a fact .
The person that I got the fact from ( a college professor) has a history of being wrong on many counts.
Especialy when he and I argued earlier today about the true origins of the Native Americans. ( i wont go into it,, he is now in my book, a bloody twit).
Most of the native tribes in America were the Clovis people originating in Soouthern Gaul ( around what is known now as Marsaiels ( sp)).
