Created by Jez and Tom Butterworth and James Richardson, the Sky original drama follows the clashing civilisations and religions in the mythic world of Britannia, where Celtic tribes, psychedelic druids and brutal Romans battle to claim hold of the state.

Sophie will star as Hemple, the wife of Roman General Aulus, played by David Morrissey (The Singapore Grip). When her husband fails on his mission to capture Cait, the chosen one, Hemple steps in to finish the job.

Series three of Britannia will also see the return of Mackenzie Crook (Detectorists), Annabel Scholey (The Salisbury Poisonings), Nikolaj Lie Kaas (Face to Face), Julian Rhind-Tutt (Harlots), Eleanor Worthington-Cox (Hetty Feather) and Zoë Wanamaker (My Family).

Sophie Okonedo said: “I’m so glad to be plunged into the weird and wonderful world of Britannia. I was already a fan of the show and its writers Jez and Tom Butterworth, so I jumped for joy when they offered me the wonderful character of Hemple.

“Without giving too much away I’ll just say this woman has a huge appetite…”

Series co-creator James Richardson added: “Sophie is one of the UK’s greatest actors and we all feel very privileged to have her play our new and particularly malevolent force for series three.

“She is an actor with an enormous range and manages to make you laugh whilst being completely terrifying. A perfect fit for Britannia!”