A History of Celtic Britain (2011) BBC

Episode 3: Age of Invasion

Continuing his epic story, Neil Oliver explores the remains of brutal Iron Age battles and Celtic rebellion as he reaches the moment when Celtic Britain was ripped apart by the world's great empire - 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