Although I'm not sure how far back you're looking, I'll start with the Bronze Age immigrants to Britain known as the Beaker People. Originally from Spain, these travelers ventured over in approximately 2500 BC, and flourished on the British Isles. They constructed elaborate gold and bronze jewelry, as well as detailed stone circles, the best known of which is Stonehenge. There were two waves of Celtic immigration to England. The first is popularly known as the Goidelic Migration, which occurred between 2000 and 1200. The next is known as the Brythonic migration, which most likely took place between 500 and 300

http://www.ucl.ac.uk/archaeology/research/directory/beaker-people-parkerpearson