Dia Dhuit!

It would certainly make sense that the majority of the population of the British Isles would be ultimately descended from Megalithic stone-builder peoples. Later invaders (Iberian Celts, Angles, Saxons, Jutes, Normans, Danes, etc.) would have left a relatively small physical mark on the indigenous people. However, they DID leave a huge cultural mark. That would be assimilation.

"He also adopts Dr. Forster’s argument, based on a statistical analysis of vocabulary, that English is an ancient, fourth branch of the Germanic language tree, and was spoken in England before the Roman invasion."

I wouldn't say this some new-fangled argument. It's generally well-known that English is a Germanic language. Structure is what defines a language, not borrowed vocabulary. As for some form of English being spoken in England before the Roman invasion, I think that's probably nonsense. The Angles, Saxons, and Jutes arrived in Britain after the Romans left.

"Historians have usually assumed that Celtic was spoken throughout Britain when the Romans arrived. But Dr. Oppenheimer argues that the absence of Celtic place names in England — words for places are particularly durable — makes this unlikely."

Absence of Celtic place names? What about Avon? What about London?

"The Celtic cultural myth “is very entrenched and has a lot to do with the Scottish, Welsh and Irish identity; their main identifying feature is that they are not English,” said Dr. Sykes, an Englishman who has traced his Y chromosome and surname to an ancestor who lived in the village of Flockton in Yorkshire in 1286."

I can't believe that in 2007 someone would make such an arrogant, dismissive claim as that. Cultural myth? Evidently the esteemed Dr. Sykes is unaware of such culturally defining features as language, dress, food, music, and other customs. I guess the defining feature of the French people is that they're not English!

As an Irishman, I don't define my "Irishness" as being "non-English" or even "anti-English." That would just be stupid and antagonistic. What's so wrong with English culture anyway? I like Fish and Chips, Bangers and Mash, and Yorkshire Pudding! I like traditional English folk music and I enjoy English history and literature! I don't need to define myself as "not English" because I am not English!