First up: there is no archaeological evidence at all. That cannot be stressed too heavily.

What we then have are only three literary references, all from Romans.

Two of them seem to me meaningless in a rigorous historic analysis.

Caesar mentions he had "heard" that Druidism in Gaul may originally have come from Britannia. Well, Caesar mentions in Bello Gallico a LOT of nonsense the locals spouted to him. He doesn't seem to have taken it very seriously, and it would be weird if we did 2 millennia later!

Strabo's reference does not even mention Britannia (or Hibernia). Merely that Druidism had "spread from Gaul across the sea". Neo-Druidists pounce on this as evidence that the religion spread to Britain. Note, however, that this Strabonic piece of gossip is almost the exact opposite of the Caesarian piece of gossip!!! Hence, it is pretty useless, historically.

We are now left with Tacitus, and his description of the subjugation of Anglesey.

Go get the text, read it, and then tell me that Tacitus is seriously depicting a Druidic cult in Britannia (let alone the claimed "Druidic Capital of Europe") that apologists now claim.

He seems little interested in Druids, and much more interested in the dark-haired female harpies, doesn't he?

If Tacitus is 'hard evidence' for a Druidic presence in Britain, then Eric von Daniken is Gospel, quite frankly.

In short - NO meaningful evidence exists for the existence of the Gallic Druidic cult in either Britain or Ireland.
Those who have linguistically tracked down the 'nemetons' even into central Turkey, should explain why they have not found the nemetons of Britain & Ireland, no?

PL