Mistresses star Sarah Parish reveals the evil behind the medieval mother she plays in C4’s lavish adaptation of Ken Follett’s novel, Pillars Of The Earth…

What’s it like to play a woman as evil as Regan Hamleigh?
“I love Regan, she’s fantastic. She is such a brilliantly bad person and has some wonderfully cutting lines. She has no redeemable features – she’s just pure evil, brilliantly and beautifully evil. You really look forward to the scenes where she does all her plotting and mischief.”

Were you surprised to be cast as Regan?
“Yes I was slightly surprised. I read Ken Follett’s book about two years ago and in it Regan was described as being the most hideous awful creature that anyone had ever set eyes on. You could barely look at her she was so ugly. She was covered in boils, no teeth, stick thin; she looked like she could break and barely any hair left. Luckily in this I was just ‘Hollywood ugly’ so I got away with a birthmark on my face!”

You’ve got some incredible medieval costumes, what did you think of them?
“Regan’s costumes were beautiful, and all handmade by the designer. Mine changed in size quite dramatically over the time we were filming because I was pregnant, so I needed the same dress, but just a bit bigger every week, so I could get my bump into it. Although the dresses were magnificent, they were quite uncomfortable and heavy to wear because the heat in Budapest when we were filming was very intense. They hid my pregnancy really well with the clothes and fans. I actually gave birth 48 hours after I finished filming!”

How did you find the experience of filming while you were pregnant?
“I was very lucky as I didn’t discover the pregnancy until quite late on, so for the first half of filming I didn’t even know I was pregnant. My daughter Nell arrived a bit early, too, so it was actually like the shortest pregnancy in the history of the world. And it was incredibly easy. It’s great to be working while your pregnant because you’re sitting around all day stuffing your face, and not thinking about when you feel ill. You’ve just got to get on with your work. Everybody in the cast or crew was incredibly supportive. So I didn’t have the usual problems of morning sickness or cravings and stuff.”

Do you bring Nell on set now when you’re filming?
“I have a nanny and brought her along for when I filmed Mistresses a few months back – she comes with Nell everywhere I go. I try not to have her on set, though, as she’s very little and it’s very boring.”

What was it like to film in Hungary?
“There were some wonderful locations, but we did leave Budapest for Vienna in Austria to do a lot of filming involving the nobility of the piece. We filmed in the most incredible castle there but it was unbearably cold and uncomfortable.”

Why is Regan’s relationship with her son so incestuous?
“It’s very unhealthy relationship, isn’t it? It didn’t appear in the book like that. We were slightly worried that we’d pushed it too far, that it would offend people. In the end we kept it in because it’s a wonderful way of explaining why William is a ghastly terror. You’ve got this awful underlying relationship with his mother that has pushed him to the edge of sanity. It started with a few moments and by the end of filming there’s a full-on snog. It also works because Regan’s husband Percy, played by Robert Bathurst, is this ineffectual bumbling man. She’s repulsed by the buffoon she’s married to, so you can see why she’s so obsessed by the image of herself in her son.”

How was it doing such taboo scenes?
“You just get on and do it really. We tried to do the scenes in as subtle a way as we could without it looking garish and slightly vulgar. Ultimately the actor, David Oakes, is not my son. We had good chemistry so there was a lot of trust there to do the scenes that were, shall we say, a little more delicate.”

Was it fun working alongside Ian McShane, who’s starring as scheming bishop Waleran Bigod?
“Yes, it was great fun. Ian and I did a series together ages ago called Trust. It just a great family feeling on set if you get a cast without a***holes.”

*C4’s Pillars of the Earth begins with a double bill on Saturday, October 16