Genetic map of Britain goes on display - University of Oxford:
On the genetic map of Britain, Cornish people clustered separately from those from Devon, while the Scottish and Irish tended to share the same DNA markers. Those in South Wales formed a group, while there were separate clusters in the Welsh borders and in Anglesey in North Wales. People in Orkney were different from everyone else. In England, the majority of the South, South-East and Midlands formed one large group. Cumbria, Northumberland and the Scottish Borders seemed to share a common past. And Lancashire and Yorkshire, despite their rivalry, seemed to be as one genetically.
In the project DNA samples were taken from 4000 people whose four grandparents all came from the same area. so this does not necessarily tell about the entire UK population, but rather about those whose ancestors tended to stay put where they were born.
It would be interesting to see if a sample was taken of people whose great grandparents, or great great grandparents had all come from the same area, as the genetic variations would probably become clearer still, though it might be more difficult to find a sample as many people do not know the names of all their great grandparents, much less where they were born. I certainly didn't know the names of all mine until I started genealogical research 40 years ago.