The Iron Age is conventionally said to begin around 800 BC. The Atlantic system had by this time effectively collapsed, although England maintained contacts across the Channel with France, as the Hallstatt culture became widespread across the country. Its continuity suggests it was not accompanied by substantial movement of population. On the whole, burials largely disappear across England, and the dead were disposed of in a way which is archaeologically invisible. Hillforts were known since the Late Bronze Age, but a huge number were constructed during 600–400 BC, particularly in the South, while after about 400 BC new forts were rarely built and many ceased to be regularly inhabited, while a few forts become more and more intensively occupied, suggesting a degree of regional centralisation.

Contact with the continent was less than in the Bronze Age but still significant. Goods continued to move to England, with a possible hiatus around 350 to 150 BC. There were a few armed invasions of hordes of migrating Celts. There are two known invasions.