The British are actually made up of several distinct peoples.
The largest group is the English who are partly descended from the Angles, Saxons and Jutes, three Germanic tribes who came from continental Europe around the fifth century; party from later Norse settlers from Scandinavia and Normans from northern France (but originally from Scandinavia); and partly from the original British population.
The Scots, who live in Scotland, are mostly descended from Irish settlers and Picts, the original inhabitants of northern Scotland, as well as some Anglo-Saxon and British elements.
The Welsh could be considered the original British people. Although they now live in the small nation of Wales, the earliest historical records indicate that their ancestors once inhabited all of what is now England and southern Scotland as well. Archaeology has not yet established with certainty where they came from, or when, but their language is related to that of Celtic tribes which formally inhabited continental Europe.