Playing Brona in Penny Dreadful brought a few challenges for softly spoken, plummy-toned Billie – not least learning the much harsher Northern Irish accent. Shooting the show in Dublin didn’t help, as she found the variations confusing at times. Billie said: “I had a hardcore dialect coach. It’s Northern Irish but it was hard being in Dublin with loads of Dubliners on the set.

“It’s really unhelpful because lots of us are doing different accents, so she was a permanent fixture. Sometimes, I’d practise round the house and we’d listen to a lot of it in my car. My kids would find it really funny. We’d all do it together in my car to a CD and, yes, they loved it.”

In fact, Billie got so good at the harsh Northern Irish accent, she had to tone it down for fear viewers wouldn’t understand her. “Because it’s a very strong accent, as you know, and a hard accent as in how it sounds, it’s sometimes hard to understand. I think we had to be very mindful of it being too Belfast. It was that battle of making everything you say heard but also being true to the accent. Everyone can judge it, now they can see it. God!”

Shooting in Dublin meant the cast had plenty of opportunity to let their hair down during breaks in filming. And she loved her time there so much that she is considering moving to the Irish coast in the future with her family.

“I’d like to move there for a while,” said Billie. “I wanted to do something a bit more coastal but I never managed to do anything more than go to work and then go to the pub. That’s the future, something more adventurous. I had a great time there. It was good for me because I was coming back and forth but hanging out in Dublin. We drank a lot at our hotel, which was a kind of boutique affair, and then some of the boys’ pubs on Baggot Street. Our favourite place was The Red Hen and it was around Christmas time so, yes, there were a few parties.”

“I suppose it was the thing of everyone being away from home so everybody kind of leans on each other more heavily and you build a relationship outside of work. I suppose that then informs the next day of filming. And working in a studio we had our dressing rooms next to each other so it became a bit like a drama school there – a wayward drama school. We were among like-minded people so it was just fun. I really miss it.”

As she said, Billie is drawn to strong, wild characters like Belle from Call Girl and now Brona in Penny Dreadful.And with the success of shows such as Game Of Thrones, with dominant women including Daenerys Targaryen and Brienne of Tarth, Billie believes it’s a great time for female roles on TV.

“Brona’s Irish, she’s moved to London with big ideas and a big heart. She’s hard living and hard drinking and she loves hard as well. She’s a spirited, feral thing and she’s ill. She has a fatal disease so she is living life like every day is her last and she falls in love with a kindred spirit in Ethan (Hartnett) really. It’s great there are a lot of strong women in Penny Dreadful. I don’t know if that’s conscious because of things like Game Of Thrones. I think it’s just John Logan (Penny Dreadful’s creator) creating these forward-thinking, sassy women with enormous flaws.

“Kind of what you need to see in a woman, not just some high-achieving perfect thing. The women are really well-written. They’re not just man extensions, they’re stand-alone figures.So I’d love to do another series. And then one after that and then after that. It’s such a good gig and everyone is lovely.

“You’re working with people who are really talented, so you’re keeping such fine company. I think it’s a gift of a job.”

■ Penny Dreadful is on Sky Atlantic at 9pm on Wednesday.