Which language was commonly spoken in Britain during the Iron Age?

The Iron Age in Britain, which lasted roughly from 800 BC to the Roman invasion in 43 AD, was a time when Celtic culture flourished. The people living in Britain during this period were predominantly Celtic tribes, each with their own variations of Celtic language and customs. Think of names like the Iceni, the tribe Boudicca led in revolt against the Romans – they were Celtic. Celtic languages are a branch of the Indo-European language family, and they were spoken across much of Europe before the rise of the Roman Empire and the Germanic migrations. So, while Latin would later become important due to the Roman occupation, and Anglo-Saxon would arrive much later with the Germanic invasions, Celtic languages were the established languages of Britain during the Iron Age. English, of course, didn't exist yet! It evolved from Anglo-Saxon, which is why Celtic is the correct answer here.