Article - Celtic From the West - A summary of the argument - Steven A Williams

A summary of the article "Celtic from the West" Barry Cunliffe and John Koch.

The article suggests that the Celtic homeland, rather than being in middle Europe arose in the West of the British Isles and that the Celtic languages arose as a lingua franca (descended from PIE) between the communities along the Atlantic coast. There are three strands to the evidence: linguistic, genetic and archaeological. 

Linguistic: the earliest mention of the Celts in classical literature places them along the Atlantic coastline. The distribution of Celtic place names matches well to the distribution of the communities along this coast. Analyses of Celtic languages suggest that they split from PIE ancestor before 4000 BCE. This article mentions that Tartessian (from southern Iberia) may be an ancestor of Celtic (see genetic evidence below also blog post on Tartessian as Celtic)

Genetic: genetic evidence (Oppenheimer) shows people migrating from the Iberian peninsula and settling along the Atlantic coastline. There is no genetic evidence for mass migrations of people from the 'traditional' Celtic homelands in middle Europe at the appropriate period.

Archaeological: Cunliffe shows that there was a 'flowering' of an Atlantic Cultural Zone which matches well to the other evidence.

This Atlantic Cultural Zone traded within the communities and would have required a shared lingua franca. Trade also developed with NW Europe.

The evidence for this seems solid to me, and matches well to the arguments that I am currently reading in Oppenheimer "The Origins of the British".