The Steppe nomads spread their language and culture as far as India.

The Bell Beaker people became the Celts, and enjoyed the British Isles right up until the Romans arrived and then buggered off, leaving a power vacuum that the Angles, Saxons and Jutes were happy to fill. They supplanted them in short order, driving the Celts and the Picts to the extremities of the island.

That's one theory. Some burials have been found of genetically Celtic men being buried with full Anglo Saxon honours.