From the Scotsman:

A MAJOR genetic study of the population of Britain appears to have put an end to the idea of the “Celtic fringe” of Scotland, Ireland and Wales.
Instead, a research team at Oxford University has found the majority of Britons are Celts descended from Spanish tribes who began arriving about 7,000 years ago.
Even in England, about 64 per cent of people are descended from these Celts, outnumbering the descendants of Anglo- Saxons by about three to one.
The proportion of Celts is only slightly higher in Scotland, at 73 per cent. Wales is the most Celtic part of mainland Britain, with 83 per cent.
Previously it was thought that ancient Britons were Celts who came from central Europe, but the genetic connection to populations in Spain provides a scientific basis for part of the ancient Scots’ origin myth.