ACTOR George Costigan didn’t need to think about it when he was offered a role in ITV1’s soap Emmerdale. “The producer explained what the storyline was and he was offering to pay me money to do something I’ve been doing for 42 years – which is to be in love with Liz Estensen.

“I met her as a student and I’ve always been in love with her, and she knows it.

Suddenly a bloke says come over here and earn thousands of pounds while you pretend to be in love with Liz Estensen. I couldn’t wait.”

Alas, his character in the Yorkshire-set soap broke the heart of Diane, Liz’s character, and their relationship went pearshaped after he lured her to his French chateau. Coincidentally, Costigan himself lives in France, having moved his family there as a response to the Thatcher years.

“I said you can’t play the end of the story, I’ll just play what I feel about Liz, which was so easy. It’s a great company, a lovely, lovely place to work. Such lovely people. Top to bottom, an extraordinary place. So is this theatre – a very happy place to be. I do like being back in York.”

He last appeared at York Theatre Royal in Arthur Miller’s Death Of A Salesman as Willy Loman, a role he’d nursed ambitions to play for some time. During that run, he and one of the actresses asked director Damian Cruden about putting on Blackbird, David Harrower’s play that won an Olivier award in 2007 as best new play.

He read it and agreed to stage it in the Studio theatre. Then the actress got pregnant, and so did the actress chosen to replace her. “Then we got Charlie (Covell), which was the best thing that could possibly happen,” says Costigan.

He read with all the actresses up for the part, something he describes as an “extraordinary process”, as director Katie Posner looked for some sort of chemistry between the two actors. “Katie said the other day when we were talking about it ‘Charlie was the only one who made you nervous’, but it doesn’t do to analyse things too much.”

He recalls going for an interview with director Jonathan Church for Of Mice And Men in which his co-star was Matthew Kelly. “I remember saying to the director, ‘You can cast this better than me, but you can’t cast the relationship better because I’ve known this man for 35 years.

And you can’t cast that. You can’t cast what him and I are getting for nothing’.

Someone who’s seen a previous production of Blackbird described it to me as harrowing. Costigan isn’t about to pass judgement. “I don’t know. I’ve never seen it. I’ve never done it. The difficulty is nothing to do with the actors at all. It’s to do with the writer’s job. It’s very intense.

“I can’t resist this play, it’s so beautifully written. Somebody said to me the other day, ‘What do you prefer, television or theatre?’ I like good material, I don’t give a damn where it is. This is everything one can want in a play.”

He knows that if you say the play is about the aftermath of a relationship when the girl is 12 and the man 40, most of the audience are going to say they don’t want to go to a play about child abuse.

You couldn’t blame them, he says, but they would be wrong. Not least because he feels it casts more light on the issue than others have done on a subject on which there’s no shortage of information.

“This is what theatre does better than anyone else – it illustrates it live in front of you. Emotionally.

“You can come and review it and you won’t have a choice about whether you’re engaged. When things like that happen in theatres, then theatre is doing what’s best about it.”

• Blackbird opens tonight in York Theatre Royal Studio and continues until November 12. Box office 01904-623568 and online at yorktheatreroyal.co.uk