You're currently in rehearsals for a production of Shelagh Delaney's A Taste of Honey at the National Theatre. Presumably you've seen the play before?I haven't, no. I remember from a long time ago seeing the film on television. So I have a vague memory of it, but I've never sat down and watched the whole film. And I've never seen a production of the stage play. So although I knew the name – most people I think have an idea it's about a young girl who's pregnant – I didn't know the specifics of it. So I've kind of come to it fresh. And I'm certainly not going to watch the film now.  It's surprising you've not seen it because it's a bit of a 'key northern text' and I think of you as someone from the north [Sharp was brought up in Formby] who is actively interested in northern culture. Well, I knew it was part of a canon of writing that was happening in the 50s and was a response to the old order. So I knew that it was in the same territory as Room at the Top and those sort of black-and-white British movies. But they were all part of a particular literary tradition that was very firmly established long before I started my acting career. So in a way, by the time I'd left drama school and started acting, that was all old-fashioned.  So what attracted you to doing it now? Did you think this was a great period piece or that it was very much alive and relevant?Well both, but I suppose what really engaged me was that although the play is more than 50 years old, Shelagh Delaney was saying something very truthful about a relationship between a mother and daughter, about a parent who's failing and doesn't quite know how to make it right. The period detail is that there weren't these layers of welfare system to catch women who had children. There weren't benefits, there weren't handouts, so that kind of adds an element of desperation that is part and parcel of the character of Helen.  Why do you think mothers and daughters are so often in conflict?I just think there's something about passing on the baton from parents to kids. On the one hand they want them to have it, but on the other there is something unbearable about the acknowledgment that it's passed on. And with women it's bound up with fertility, whether or not they care about that, so it's about living and dying. And this play is about a 16-year-old girl who gets pregnant, so it's all about life ahead of her. As her star, in terms of being human, is rising, [her mother] Helen's star is falling. That tension – no matter how much you love somebody – can't help but create some movement of the tectonic plates between us.  You're one of the great naturalistic TV actors [in series such as Clocking Off and Scott & Bailey], but on stage you need to project. Does that make it a very different way of acting?You have to find another way of getting a close-up, if you like, on stage. It's about a kind of pact that you make with a group of strangers who come through the door to watch. And they are as much part of what happens on stage that particular evening as the actors who are on it. It's exhilarating. I don't think there are very many people who can do it very well, working on stage. But you look at someone like Simon Russell Beale, who's doing King Lear here, and he's, you know, amazing.  So are there actors you'd go to see on stage just to see them act, regardless of what they're in?Yeah, I suppose so. You think, yeah it'll be great. It's like going to see Adrian Lester and Rory Kinnear in Othello and you think, this is going to be fantastic. And on top of that you get an amazing production as well. It's a Brucie bonus.  Acting can be an insecure profession. Have you had your moments of doubt and thought about leaving it?There have been times when the instability of it all has not been comfortable. But you know everyone has that. I suppose I'm of the school of never explain, never complain. Everyone has a certain hand dealt to them and you just have to work out whether you can keep going. The thing is, I don't know what I would do if I didn't act.  What are your chief satisfactions as an actor?The thing that gives me most pleasure is when I feel I've really engaged with my colleagues, other like-minded individuals, in getting something to work, and that I'm part of something. I suppose it's about committing to a version of a family.  You were adopted. Has that led you to seek out alternative families or a particular identity? I think it makes you at some level a strange critter. At times it's made me feel very upset, because I feel I don't know where I belong, and there's a sort of yearning and I wished I belonged somewhere. But the other side of that, which is also very good, is that you're free to be who you are. And actually it's not better, it's not worse, it just is. At different stages of your life you have a different relationship with where you're from, where you belong, where you don't belong. But at the end of the day I think you take meaning and you take nurture and you take love where it's given. And that's what's important.  Do you think it's formed who you are?Yeah I do. I don't know how to articulate it. Sometimes when I hear people talking about their families, or their relationships with their mothers and fathers, I hear it but it's not something I totally understand. My adoptive parents were terrific. But I always felt there was a world happening somewhere that I needed to roll my sleeves up and get involved with. And it wasn't where I lived. I needed to get on a train and come to London.  Did you ever meet your birth parents?I met my birth mother and we were able to have a relationship for 17 years before she died. And I think she felt very guilty for giving me up for adoption and so on. But there were very good reasons at the time and it was the way the world turned. I said, if you hadn't given me up for adoption I wouldn't be doing what I'm doing now, and actually what I'm doing now is all right and the person I am now is all right. It's like chaos theory, tiny things happen that lead to something else. You can't torture yourself.
The actor talks to Andrew Anthony about her new role in A Taste of Honey at the National – and how being adopted has shaped who she is