It’s the story of what happens when a celebrity – a guy who’s a comedian and a quizmaster – gets accused of historic sex offences. And it’s the story of how that impacts his family. For me and my character, Marie, it’s about faith, with a big ‘F’ and a small ‘f’. And it’s about truth and what that is, and loyalty, and family.

You play Marie, who is the accused’s wife. What’s she like?

They’ve been together – this is a backstory that I invented for myself but I imagine is true anyway – they’ve been together possibly since they were late teens, perhaps a little later. They’ve been together for 40 years, anyway. She is a Catholic, and she’s not one of those wives who’s interested in the limelight. That’s why they click. She’s not part of that celebrity world. She’ll be on the edges of it, on occasion, and that’s fine. But, for example, in the opening scenes he’s at an awards ceremony, which she hasn’t bothered going to. There have been too many of them.

She’s a very good and loyal person, and faith plays a big part in her life. Is it more difficult to get your teeth into a part like that than someone like Cynthia Coffin [from Indian Summers] who is deliciously malevolent?

I don’t think there’s any difference in the approach. Obviously there’s a huge difference in the characters, but I don’t think it’s any more or less difficult. Maybe it’s more obvious who Cynthia is as soon as you read it, and I suppose with Marie it’s a bit more complex. One of the first conversations I had with Mark [Munden, the director] he said “How on earth does she stay with this man?” And I could see why she did, from reading the script. It’s about faith and needing to believe certain things. And as she’s a Catholic; she won’t want her marriage to be over, despite his infidelities. It’s about forgiveness and trust, believing him when he says “I will always tell you what’s happening.” So those things had to be worked out, why is this woman where she is? It’s like when you see pictures of Rolf Harris and his wife, it’s her that I’m actually fascinated by. How is she standing next to him, holding his arm, in this?

Did you look at the stories of women who had stood by their husbands, for research?

No, but when I did see it on the news, I was fascinated by them.

What was it that attracted you to this project in the first place? You get offered a lot of stuff, why this?

I don’t get a lot of stuff like this, I have to say. It’s unusual. It’s fascinating – you can’t help but be drawn in. It’s really fascinating. How do people deal with this? I think Jack Thorne [the writer] has dealt with it in a really interesting way. There were lots of things that attracted me to this, Robbie Coltrane being one of them. And Mark Munden – that was very important, that he was doing it. It could have been pushed one way or the other, depending on who was directing it. And with Mark, it was going to be from a very interesting aspect. I felt that when I went and met him. I found him really interesting, and felt he was discussing the right things about it.

Had you worked with Robbie before?

Only on the Harry Potter films, and I think we maybe had one scene together over ten years. But I’ve met him, obviously, at things over the years. I didn’t know him, really, before this.

The subject matter is pretty sensitive and potentially controversial. Did you have any misgivings about that?

I didn’t have misgivings, because it’s truthful, there’s a truth behind it. So you can’t go wrong, really. It’s not sensationalising the issue for the wrong reasons. It’s being done for the right reasons.

Operation Yewtree and the associated scandals have been front page news for years now, and it shows no signs of going away. The series deals in part with the idea of trial by media. What are your feelings in that regard? It’s a dangerous road we’re going down, isn’t it?

Is it? I feel for people who are accused of something they haven’t done, but have been in the media spotlight because of it. It’s very difficult to get rid of that sort of thing. No matter what happens, some people will always think “There’s no smoke without fire”. That is very difficult. On the other hand, as is shown in the series, it really helps the police when things are publicised, because it tends to give other people the courage to come forward, and they can then build a case. And I think that overall, the victim has to come first, no matter what.

It’s becoming increasingly clear that there was a very unpleasant culture in the past with regards to male celebrities. That doesn’t seem to be the case so much today. Is that because the culture has changed, or because celebrities are just so much more worried by the media today?

I think both. I think the culture has changed because of that fear of exposure. I think if your sexual predilections are towards vulnerable people, or towards rape, I think that’ll always be the case. I don’t know. But I think things have definitely changed, because of all the historic sex offences cases that have come up and been prosecuted. Also, women are more liberated and there are more women in positions of power. And people are more able to speak about abuse. Children didn’t have a voice, not very long ago, about being sexually abused. They weren’t believed. It wasn’t talked about. But now people listen if a child says “somebody has touched me.” People realise that you have to talk about these things.

Do you think celebrity has a role in all of this? Is it all connected to the adulation and ego trips that celebrities are affected by? Do they end up feeling invulnerable?

Yes, I think so. And also vulnerable young women feeling safe with the person. So it’s a real abuse of that, when it happens.

One of the things that emerged in the relationship between Marie and Paul is that some aspects of their relationship work very well. And they have all this shared history. But it’s also about whether you can ever really know someone…

I think she chooses not to. She chooses to turn a blind eye. And there’s a bit of a lack of intimacy about Marie. With her daughter and also with her husband. There’s a bit of a cut-off. Maybe there’s something in her history that we don’t know about. But for whatever reason, she turns a blind eye. They are quite separate. They’ve almost worked out a deal, as long as she doesn’t know about it, or have to engage with it emotionally, then it’s fine. Also, she’s a Catholic, she’s not going to leave him. Or, at least, she doesn’t want to.

The series looks at fame and celebrity and what it’s like to live in the public eye. Obviously you have experience of that, but you seem to be able to keep your private life very private. Is that something you have to work hard at?

I think you probably have to work hard at doing it the other way, actually. But yes, I very much value it. It keeps me sane, to not live in London, to not be around it too much. I don’t go to premieres and things unless it’s my own one. I’m not interested in being photographed. There’s enough publicity around the jobs that you do.

You talked about Marie’s relationship with her daughter, who’s played by Andrea Riseborough. How did you find working with her?

She’s out of this world. I loved working with her. She’s wonderful. I found her terribly touching. I was a huge fan anyway, before we came to do National Treasure. Everything she’s done, that I’ve seen, has been fantastic.

What do you look for in a role these days?

The truth, and a story that I’d quite like to be part of, for whatever reasons. There needs to be some kind of integrity to it. I’ve got to believe that someone’s writing it because they really, really want to. Even in Paddington Bear, Paul King, the writer, absolutely adores Paddington. He loves it, and it’s great fun being on it with him. It’s that, and who’s involved. Who’s directing it and who the other actors are.

Is there anyone who you’ve always dreamed of working with? Do you have any unfulfilled ambitions, be it a role you want to play or someone you’d like to work with?

Not a role, because it depends so much on who’s directing it and what the script’s like. There’s loads of fabulous roles, but you think “No, this doesn’t work,” or you don’t like the idea of working with this person. I have an ambition to carry on, that’s about it really – whatever that means. I like to see what comes up.

Are there any roles that you’ve turned down that you’ve bitterly regretted?

I don't think there are, really. I have turned things down that have become very successful, but I thought “No, she’s much better in it than I bloody would have been.”

Do you think that anything you ever do, for the rest of your career, is ever going to match up to the two soups sketch?

[Laughs] No!

Have you ever served soup at home like that?

[Laughs] No. But anything that I do now, for example in Indian Summers I had to carry a tray, and the cast were all laughing away at me. I can’t get away from it. But I don’t want to get away from it either.