People living in the British Isles and most of north-west Europe are descended from people who came in from the south, repopulating these islands after the Ice Age 9,000 years ago. One distinct group includes present-day Basques and the population of Sardinia. Genetically they and the Sardinians seem to be unrelated to their neighbours. Many races such as the Celts, appear to have no genetic basis whatever. There are far more similarities.
Most differences are cultural.
It's what people call themselves. Look at the Serbs and the Bosnians - genetically they are identical. In Ireland genetically the Protestants and Catholics are identical. We share many similarities with the French and Germans. The research was carried out by Professor Ornella Semino of Pavia University, Italy, and colleagues in Russia, California, Sweden and Greece.