Thanks for reading and taking the time to respond, Duncun. I haven’t seen the documentary but I’m surprised to hear that the BBC presented things that way. Perhaps it’s another case of the winners get to write history or the documentary producer was a fan of Tacitus.
There also appears to be only a limited archaeological record regarding the Druids, so not much to be gleaned from there either. Still, the Bardic tradition lives on in Wales so culturally they could be said to have left an impact.