Britain was of course known to traders from the Mediterranean and may have been reached from Gades or Tartessus by Phoenician, Carthaginian and Greek traders. There is however, no hard evidence for this and Greek coins found in Dorset and Devon are not proof of direct contact. There is abundant evidence for trade with Gaul.
Metals will have been very important due to the relative scarcity of tin required to make bronze. Competition for the control of this trade must have been fierce. Cornish tin was exported by sea to Corbilo on the mouth of the Loire and thence across Gaul to Massalia. The Veneti of Aremorica seems to have dominated this trade at the beginning of the historical period, until their conquest by Caesar disrupted the ancient routes.
Hengistbury head was an important marketplace for Aremorican pottery and undoubtedly other trade goods from Britain. Mediterranean wines were reaching the homes of high status individuals in southern and western Britain by the middle of the first century BCE.
The conquest in 58 BCE of Gallia Comata by J Caesar brought the Romans into indirect political contact with the Celtic speaking communities in Britain. Military assistance was provided from Britain to the Belgic opponents of Caesar and the Belgic gold coins from the series labelled E appear in southern Britain in large quantities. These coin imports may mark payments made for British military assistance and the personal wealth of high status Belgic leaders who fled to Britain to escape Roman pressure. It should be recalled that gold coinage was struck as bullion and not for commerce.