Let's say that Stephen Oppenheimer was very wrong. As I said, it was originally thought that R1b originated in the Iberian penninsula during the last ice age, however it is nowadays thought that R1b arrived in Europe only 8000-4000 years ago.
Also, Oppenheimer was unaware of the vast differences in the R1b subclades. The claim that the dominance of R1b in Britain "invalidates the Anglo-Saxon wipeout" theory is also wrong, since there's a huge difference between the R1b subclades U-106 (associated with the Germanic peoples, accumulated in England by the Anglo-Saxon invasion) and the subclade M-153 (associated with Basques). There's also a difference between the various Celtic R1b subclades and U-106.
Also, I am afraid to say this, Oppenheimer is an eccentric, and based on his (outdated) finding he formed some very crazy ideas, including the idea that the English "have always been there", and that English was spoken in Britain before the Roman period, which of course is totally ludicrous.
What about Bryan Sykes:
In his 2006 book Blood of the Isles (published in the United States and Canada as Saxons, Vikings and Celts: The Genetic Roots of Britain and Ireland), Sykes examines British genetic "clans". He presents evidence from mitochondrial DNA, inherited by both sexes from their mothers, and the Y chromosome, inherited by men from their fathers, for the following points:
The genetic makeup of Britain and Ireland is overwhelmingly what it has been since the Neolithic period and to a very considerable extent since the Mesolithic period, especially in the female line, i.e. those people, who in time would become identified as British Celts (culturally speaking), but who (genetically speaking) should more properly be called Cro-Magnon. In continental Europe, this same Cro-Magnon genetic legacy gave rise to the Basques. But both "Basque" and "Celt" are cultural designations not genetic ones and therefore to call a Celt "Basque" or a Basque "Celtic", is a fallacy.
The contribution of the Celts of central Europe to the genetic makeup of Britain and Ireland was minimal; most of the genetic contribution to the British Isles of those we think of as Celtic, came from western continental Europe, I.E. the Atlantic seaboard.
The Picts were not a separate people: the genetic makeup of the formerly Pictish areas of Scotland shows no significant differences from the general profile of the rest of Britain.
The Anglo-Saxons are supposed, by some, to have made a substantial contribution to the genetic makeup of England, but in Sykes's opinion it was under 20 percent of the total, even in southern England.
The Vikings (Danes and Norwegians) also made a substantial contribution, which is concentrated in central, northern, and eastern England - the territories of the ancient Danelaw. There is a very heavy Viking contribution in the Orkney and Shetland Islands, in the vicinity of 40 percent. Women as well as men contributed substantially in all these areas, showing that the Vikings engaged in large-scale settlement.
The Norman contribution was extremely small, on the order of 2 percent.
There are only sparse traces of the Roman occupation, almost all in southern England.
In spite of all these later contributions, the genetic makeup of the British Isles remains overwhelmingly what it was in the Neolithic: a mixture of the first Mesolithic inhabitants with Neolithic settlers who came by sea from Iberia and ultimately from the eastern Mediterranean.
There is a difference between the genetic histories of men and women in Britain and Ireland. The matrilineages show a mixture of original Mesolithic inhabitants and later Neolithic arrivals from Iberia, whereas the patrilineages are much more strongly correlated with Iberia. This suggests (though Sykes does not emphasize this point) replacement of much of the original male population by new arrivals with a more powerful social organization.
There is evidence for a "Genghis Khan effect", whereby some male lineages in ancient times were much more successful than others in leaving large numbers of descendants.
is he wrong also?