This
http://www.writer2001.com/cihoards2.htmgives us some very useful pointers.
"Hoards of coins found in Jersey include coins from the Durotriges (= Dorset and SW Hampshire)... An important Durotriges site, Hengistbury Head, is where the largest concentrations of Coriosolite coins in England were found. "So both sides of the Channel have coins from the other side, and were trading with each other.
"Hengistbury had been an important port of entry for products from the Roman world, particularly wine. From the dates of amphorae found in that region, we see that Caesar's invasions put an end to Hengistbury's wine trade, and subsequent importation of wine and other goods are primarily found north of the Thames. Cassivelaunos, leader of the British forces and whose stronghold was north of the Thames, surrendered to Caesar in 54 B.C. Whether Cassivelaunos or one of his successors negotiated future trade benefits is difficult to say, but the losers were the Durotriges. ""The old trade route from Alet (St.Malo) in Brittany via the Channel Islands to Hengistbury, although ceasing to provide Britain with wine, still had its uses. Alet had storage facilities for grain - a plentiful commodity in southern Britain, but less so in Brittany, where much of the land was unsuitable. "Wine going north, and grain going south, until the Romans took over.
"The fortunes of the Durotriges seem to have declined at an alarming rate: their coinage started in gold of a slightly lower standard than British A, and then deteriorated in quality from base gold through silver to billion and finally ending in bronze "Collapse of the ME in this part of the world.
The pre-war trade route from Alet to Hengistbury included Jersey. Alet came to a violent end in about 15 to 20 AD: the reasons are unclear. The end of Alet possibly signified the end of trade with the Durotriges, which could have forced the final debasement of their currency to that of bronze.