A History of Celtic Britain (2011) BBC

Episode 4: Age of Romans

Neil Oliver completes his epic journey through thousands of years of ancient history with the modern marvels of Rome. He digs beneath a London tower block, discovers building work from a massive stadium, and encounters the remains of an African woman who lived in York 1800 years ago - all evidence of the extraordinary multicultural modern world of Rome.

In four chapters, largely based on and illustrated with archaeological finds and sites, Neil Oliver explains how, as far as is known, the Iron Age Celtic tribes known as the Ancient Britains evolved and entered European civilization. Their internecine tribal phase was warlike and partitioned. Overseas contacts, especially metal trade, brought wealth and progress. Ultimately, it attracted the superior Roman empire, which would conquer and pacify Britain into a province, like Gaul shortly before, but Caesar's invasion wasn't the definitive annexation yet, that was left to emperor Claudius; even afterward some Celtic traits and even rebellions remained.
Source: imdb.com