How is R-U152 in Britain?

[Birchy]

Whilst this Alpine Celtic marker is relatively rare in Britain, it's presence unsurprisingly peaks in the South East at around 11 to 15%. There are a multitude of possible answers including Belgae, Romans, Anglo Saxons, Normans etc, which one is the most likely source?

[Peterski]

It probably correlates with France Iron Age ancestry.

[J. Ketch]

I would say it goes back to the Late Bronze Age migration that introduced Celtic language to Britain, and replaced half the population of Southern Britain. Whether or not that is the source of the majority of R-U152 in Britain today is hard to say with all the later Celtic and French migration, but I'd guess that is the largest single source.