I recommend Syke's newest book too: Saxons, Vikings, and Celts: The Genetic Roots of Britain and Ireland . A very good book and easy to read. Oppenheimer's is the better of the two though.
Just finished that one a couple of months ago. All of his are excellent. For my birthday I am giving myself an analysis from his group at Oxford, figuring I can share it with my sister, at least! I will have to dip into Oppenheimer.