This BBC article reports on a genetic discovery by the Francis Crick Institute, co-authored with Prof. Barry Cunliffe, which shows a new genetic trait arriving in Kent and then, after a pause, spreading throughout England. It did not spread into Scotland and there is not enough data to show whether it moved into Ireland.
It is possible that it either brought the Celtic language with it. Or did it bring the Brythonic version of Celtic to England, leaving Scotland and Ireland speaking the pre-existing Goidelic version of the language branch?
The article also discusses the spreading of a gene for tolerance to lactose which spread rapidly, suggesting it must have contributed greatly to genetic survival. They postulate some existential threat during the Bronze Age which allowed those who could drink milk to survive much better than those who did not.