The Bell Beaker people arrived in Britain from the lower Rhine around 2,500 to 2,300 BC with copper tools and weapons, horses and their Indo-European language and nearly completely replaced the Neolithic farmers who were still in the Stone Age. Over the next few centuries, there was a gradual transition from copper to the use of bronze tools and weapons.
The Bronze Age lasted in Britain from around 2,200 BC to 800 BC. The forests of the Paleolithic were cut down with bronze axes and the land was parceled up and converted into mass farming systems. The population exploded. Elite groups emerged and ruled over more complex societies. Then around 1,200 BC, the climate in Britain became significantly wetter and there was a period of cultural decline as agriculture became more difficult and the population shifted into the fertile river valleys from the uplands and lowlands. The Atlantic bronze networks collapsed and people increasingly began to dispose of bronze tools as offerings in wetlands. The population of Britain seems to have declined in this Dark Age which lasted until around 800 BC.
Fundamentally, little has changed in Britain since the arrival of the Indo-Europeans around 2,500 BC. Celtic languages spread into Britain during the Iron Age before the Roman conquest, but there was no replacement of the population. The Romans came and brought their Latin culture and similarly had little genetic impact on the population. Only the Anglo-Saxons left their mark and even they didn’t replace the preexisting British population. The Britons and the Anglo-Saxons were both descended from the same Bell Beaker population and had only diverged two thousand years before. The Vikings came but had almost no genetic impact on the population either because the English and the Danes had only diverged four centuries before.