The British Iron Age is a conventional name used in the archaeology

Archaeology

Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...

 of Great Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

, referring to the prehistoric and protohistoric phases of the Iron-Age

Iron Age

The Iron Age is the archaeological period generally occurring after the Bronze Age, marked by the prevalent use of iron. The early period of the age is characterized by the widespread use of iron or steel. The adoption of such material coincided with other changes in society, including differing...

 culture

Culture

Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...

 of the main island and the smaller islands, typically excluding prehistoric Ireland

Prehistoric Ireland

The prehistory of Ireland has been pieced together from archaeological and genetic evidence; it begins with the first evidence of Mesolithic hunter-gatherers settling in Ireland around 7000 BC and finishes with the start of the historical record, around AD 400. The prehistoric period covers the...

, and which had an independent Iron Age culture of its own. The parallel phase of Irish archaeology is termed the Irish Iron Age.
The Iron Age is not an archaeological horizon of common artefacts, but is rather a locally diverse cultural phase.

The British Iron Age lasted in theory from the first significant use of iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 for tools and weapons in Britain to the Romanisation of the southern half of the island.