Mick Harper wrote: It still remains to discover who was copying whom though.
I refer my honourable colleague to the answers provided by Celtic Coins.
"Celtic coinage was minted by the Celts from the late 4th century BC to the late 1st century BC. Celtic coins were influenced by trade with and the supply of mercenaries to the Greeks, and initially copied Greek designs, especially Macedonian coins from the time of Philip II of Macedon and his son, Alexander the Great. Thus Greek motifs and even letters can be found on various Celtic coins, especially those of southern France."
https://en.wikipedia.org/wiki/Celtic_coinage
There's another topic : the supply of mercenaries to the Greeks.
'ello Doris dear, I'm home from the Hellenics.
Yeah, we sorted them out, proper job.
'ere, have a look at these funny shiny metal things they gave us.
You want Provenance?
Here
http://www.celticcoins.ca/coin.php
Thousands of 'em, and coin hoards. Especially the Durotriges in Dorset. : https://en.wikipedia.org/wiki/Durotriges
And the Dobunni round Bristol : https://en.wikipedia.org/wiki/Dobunni
Unless they were all forgeries made by Harpo's ancestors in the Channel Islands?