02/07/2014 12:14 BST | Updated 01/09/2014 06:59 BST

Maggie Gyllenhaal Interview: Star Talks New BBC Series 'The Honourable Woman', Living In London and Future Plans

The Secretary star joined me in central London to discuss The Honourable Woman - her most challenging role - as well as London life and future plans with her actor husband, Peter Sarsgaard.

The path from film to television is a well-trodden one, yet the decision of indie royalty Maggie Gyllenhaal to star in an eight-part BBC series about the Israel-Palestine conflict still raises eyebrows. Until you see The Honourable Woman, that is. It's just the sort of dense and layered character piece that only television can provide, and Gyllenhaal rises to the challenge gloriously. Nessa Stein (Gyllenhaal) is the daughter of a Zionist arms dealer who subverts his legacy, spending his fortune on laying communication cables in the West Bank and making powerful enemies in the process. The Secretary star joined me in central London to discuss this - her most challenging role - as well as London life and future plans with her actor husband, Peter Sarsgaard.

Nessa looks an intense part to play. Do you find roles hard to shake off?

I learned more about myself doing this than I ever have doing anything else. I feel like a different actress and a different woman to when I started it: when I got back to New York at the end of the shoot, I went down with a fever for five days. Then, three weeks ago, I was grocery shopping and listening to 'Unluck', this James Blake song I'd listened to a lot at the beginning of filming, and mourned it in a way I hadn't before. I remembered how much I missed Nessa and all the people involved. Growing and learning is often pretty painful. But so great, in so many ways.

What did you learn about yourself during filming?

Nessa is performing herself to herself and everyone else, not even knowing she's doing it. I could understand that. As the piece goes on, that performance becomes impossible to keep up. She's trying to do good, and what good means to her changes. The idea of drawing a clear line between good and bad explodes in her face.

Is it brave to address a subject this incendiary, or necessary?

I had to think very carefully to make sure the piece wasn't saying, even inadvertently, something I didn't believe in. People in the United States and the UK are hungry to think about it and talk about it, and be led by a trustworthy, compassionate, thoughtful leader. Hugo [Blick, series creator] and Nessa offer that opportunity.

Where do you stand on the issues?

My political point of view would only keep this drama from doing everything it could possibly do. What Hugo puts forward in this drama about inheritance, peace, war, anger... They're all things I absolutely believe in.

That's very diplomatic...

Well, it's not that I don't want to upset anyone. It's that I want people to be moved, I want people to come into this piece with hearts and minds open. If you have a hardline stance, you're not totally thinking.

Does London feel like a second home after being at RADA in the '90s?

I was at RADA for a summer, and they made it very clear when we left that we were not ever to say that we went to RADA [laughs]. But yeah, it does. I love London and I have some real friends here now.

Does the push-pull of work and family life get easier for you and Peter?

No [laughs]. That's so much of what we talk about all the time: if you're going to take that project, I'll need to be home then, so maybe they can shift this date by three days... It's a constant negotiation.

How would you compare London and New York?

It depends on my mood. At the moment I love London. I would love to live here. If you speak English and you're an actor, I feel like this is where you should live. There's a general intelligence in both cities, but London feels more easygoing - people aren't fighting so hard. It feels smaller - you make something good like this and people will see it. In the States, it's a constant fight to get things seen.

Are the roles you're getting more challenging as you get older?

I think so. Yes. [laughs]

Is that surprising, given the assumption that rewarding parts dry up for older women?

I always imagined the parts that would really excite me would come in my thirties. Maybe even my forties. That's when I would be an actual woman. And Nessa is the most vulnerable person I've ever come across, and angry and beautiful and ugly, and so many things that every woman is. I hadn't ever had the possibility to express all those things. I don't know if that has to do with being 36, or just luck.

How do you follow a role like Nessa?

I've been turning everything down! I'm gonna do Tom Stoppard's The Real Thing on Broadway, which I'm excited about. It'll be quieter than Nessa. But I do feel spoilt by this.

Would you act with Peter or Jake again?

Peter is writing a movie for me that he's going to direct and maybe act in. It's the kind of thing we could make for half a million dollars by ourselves, owe nothing to anyone and really do the kind of work that we love. I always want to work with Peter, but it's a complicated line we have to walk. We don't want to play lovers onscreen - who wants to see that? But we've done two plays as people having an affair, which was very interesting. We can't play brother and sister because that would be too weird, but there are things we can play without it being like people are coming into our home. I really would like to act with my brother again, but I have the feeling we're not ready yet. We'd need to have a director and a script that we absolutely trusted. And a project that was saying something that made it worth using our actual relationship. It's not out of the question, but we have to be very careful, you know?

The Honourable Woman starts on 3 July at 9pm on BBC2.