“Jez has never seen an episode of Game of Thrones,” Mackenzie Crook tells me, laying to rest the numerous comparisons that have been drawn between the HBO juggernaut and Jez Butterworth’s new historical drama Britannia, set during the (second) Roman invasion of Britain. Crook plays Veran, a druid partial to sacrificing kings and attempting to contact the dead, in Butterworth’s series. Face tattoos and warpaint abound, as do sacred groves and stone circles, as a three-way conflict develops between the Celtic tribes of the Cantii and Regnii and the invading legions under Roman general Aulus Plautius.

And he’s right—beyond the swords and wigs, and the generally unfettered sex and violence, Britannia is lighter-hearted, faster-paced and more colourful—both literally, on screen, and in terms of influences—than Game of Thrones. Magic appears to exist, but in the more low-key guise of demonic possession and drug-induced visions of the underworld than dragons, shadow-babies or White Walkers. A vein of 1970s psychedelia runs through the show which Crook describes as “sort of the trademark, to an extent, of Jez’s writing”, replete with almost Flower-Power pink-and-purple opening credits set to Donovan’s “Hurdy Gurdy Man”. “I don’t think I even realized when we were reading the scripts, or even when we were making it, just how prevalent that psychedelia would be,” he says. “I love it. It surprised me when I saw it, and delighted me.”

Featuring, alongside Crook, the home-grown acting talents of David Morrissey, Ian McDiarmid, Zoë Wanamaker and Kelly Reilly, the whole affair feels very distinctly British, much like the other roles—namely Gareth in The Office and Andy in Detectorists—for which he is known. “I don’t know if it’s a conscious thing.” He pauses to think, as he tends to do before speaking. Understated yet insightful, Crook considers his words deliberately, and often concludes on a self-deprecating note or with a laugh. “It might stem from something as simple as the fact that I can’t do an American accent! But I can trace it right back to working with Jez Butterworth on Jerusalem nearly 10 years ago. That was an awakening for me, working with him, working on that play.

“It was so rooted in the mythology and the lore of the English, of rural England, and it was an awakening of this appreciation of where I lived. It has sort of been a passion of mine since then.”

A love of the English countryside will be apparent to anyone who watched Detectorists, whose third series recently concluded on BBC4. Crook wrote and directed the series, which follows the gently comic exploits of the fictional Danebury Metal Detecting Club, and he starred in it alongside Toby Jones.

“Detectorists very much came from Jerusalem,” he says, “and I told that to Jez early on. I said, ‘You will recognize some things in this,’ because it was inspired by Jerusalem. And there is the continuity of that through to Britannia, which is, obviously, also written by Jez.”

Far from restricting itself to English rural influences, Britannia uses Welsh when characters dabble in charms, rituals and the psychedelia-informed magic that infuses the programme. A character might mutter a spell whilst trying to make himself invisible to Roman scouts, or call on the gods to send a demon to kill her rivals for power. “I didn’t think [of] it at the time,” Crook admits. “I had to learn whole swathes of it, but nobody told me it was Welsh! I put my own inflection, my own pronunciation on it, without realizing I was messing with a real language. But apparently, I got away with it.”