‘There’s nothing safe about this place’

armour and Wanamaker’s outfits taking inspiration from the British Museum.

“It’s a flight of imagination based on reality,” Wanamaker, 68, says. “I was originally from America, and when we first came to this country my mother would tell me, ‘The British are barbarians, they painted themselves blue.’ So I ended up proving her right!”

However the biggest transformation of all was Mackenzie Crook, 46, who spent up to five hours a day in the make-up chair.

“We managed to get it down to three and a half hours at the end!” he laughs. “I grew to really love it... Slowly changing in front of the mirror was a ‘getting into character’ thing.” but we’re certainly intellectual equals.”

“My favourite bit was the night shoots where the explosions happened!” Zoe declares. “Towards the end, there’s an attack on my camp so they had to set off all these explosives. That was great fun to watch!”

For Reilly and Crook, it was shooting at the specially-built ritual site “Amber Palace’.’

“It looks like Stonehenge and we had 300 extras dancing and playing drums and a smoke machine going under a full moon!” says Reilly, 40. “I was just thinking, ‘This thing is touched with some magic.’”

Mackenzie recalls standing on top of the Amber Palace “to perform this massive ritual”.

“I just stepped away from myself and said, ‘This is quite possibly how it actually was back then.’”

All episodes of Britannia will be available at once on Thursday, January 18, on demand with Sky Atlantic and NOW TV.