Philobiblon

… but it seems Britons are predominately genetically Basques, descended from the settlers who arrived in Britain from about 12,000 to 7,000 years ago (before the land bridge to the rest of the Continent was broken).

The English still derive most of their current gene pool from the same early Basque source as the Irish, Welsh and Scots. These figures are at odds with the modern perceptions of Celtic and Anglo-Saxon ethnicity based on more recent invasions. There were many later invasions, as well as less violent immigrations, and each left a genetic signal, but no individual event contributed much more than 5 per cent to our modern genetic mix.