TIP FOR SCOTTISH PLAYWRIGHTS. If you want to have a landmark hit, just use the word "black" in your title. It's a trick that worked for John McGrath in the 1970s with The Cheviot, the Stag and the Black, Black Oil – listed at number two in The Scotsman's 20 Scottish theatre events of all time – and it's currently working for Gregory Burke, whose Black Watch, having done the military two-step all the way from New York to Sydney, is now marching on London.
You would think it would be hard to beat that show's international acclaim, but there's another "black" titled play doing exactly that.
Blackbird stormed Edinburgh International Festival in 2005 and has gone on to conquer the world. David Harrower's contentious two-hander might have attracted fewer headlines than Black Watch, but The Scotsman's theatre critic, Joyce McMillan was not wrong when she called it "mighty and timeless".
Transferring to London in Peter Stein's striking production, it went on to win an Olivier Award for best new play. Scarcely had the clamour died down than a new production on Broadway was welcomed by the New York Times as "a drama that promises to be the most powerful of the season". It is now in the running for four Lucille Lortel Awards for Outstanding Achievement Off-Broadway.
At the end of last year, Blackbird was the play Cate Blanchett chose as her calling card as she prepared to become joint artistic director of the Sydney Theatre Company with her husband, Andrew Upton.
Her production of what the Australian newspaper described as a "shocking, compelling and morally challenging" play showed what the critic regarded as "great sensitivity for the rhythms and silences of Harrower's spare, fragmented but theatrically poetic dialogue." It was a hit in Australia and again at the New Zealand International Festival.
And these productions are merely the most glamorous in a vast array of stagings around the world. Blackbird has been seen in Ireland, South Africa, Brussels, Greece, Argentina, Poland, Japan, Norway, Sweden, Finland, Mexico and Croatia. In the forthcoming months, there will be productions in France, Auckland, Oregon, Minnesota, Cincinnati and Toronto.
"I think there's also a South Korean production and I've never reached there before," says a delighted Harrower at home in his Glasgow Southside flat. "I got a letter from a schoolgirl in New Zealand the other day, saying she'd suddenly realised what theatre can be."
It's a tour of duty with which Black Watch couldn't hope to compete and that's before we get on to a possible movie version (Harrower is working on a screenplay for Jean Doumanian who produced Woody Allen's Mighty Aphrodite and Sweet and Lowdown) and a second UK production starring Dawn Steele and Robert Daws.
That show, which recently opened in Kingston upon Thames and is ending a national tour at Glasgow's Theatre Royal in June, has been received with no less enthusiasm. The Times called it "sensitive, steely and relentless", the critic of the Telegraph found himself "once again blown away by the play's power and daring" and the Guardian said it had "lost none of its visceral power".
"It's got a life of its own," says Harrower, whose translation of Brecht's The Good Soul of Szechuan is about to open at London's Young Vic in a production starring Jane Horrocks. "It stands up. I hate the phrase, but someone said it was almost 'director proof'. It's got such a draw to it that it pulls people in anyway. I haven't seen a bad review of any production yet."
The reason the play works so compellingly is the unresolved dilemma at its heart. Harrower, who is now working on the National Theatre of Scotland's 365 for the Edinburgh International Festival, faces us with a rivetingly simple question: what would happen if a 27-year-old woman were to meet the 55-year-old man with whom she had had an affair 15 years earlier? She would no longer be a 12-year-old and he would be a chastened older man with a new name and a prison record. They would have a shared story, suddenly interrupted by his arrest, and the memory of a relationship that lay somewhere between abuse and affection.
To call it a play about paedophilia would be to underestimate the cross-currents of emotion that leave the audience reeling. Harrower denies us the comfort of thinking either character is wholly right or wrong. You can feel an audience take a collective intake of breath and we leave the theatre with our tabloid certainties upturned.
"Now that people know what the play is about you'd expect some of the tension to dissipate," says Harrower. "They know what they're going to get and yet there's still that silence. It gives me a shiver that a story between two people still manages to arrest audiences in that way."
"The silence is palpable," agrees Dawn Steele, but if playing Una, the young woman, has been getting under her skin, she's showing no signs of it. When we meet at her agent's offices in central London the day after the press night, the star of Monarch of the Glen and Sea of Souls is looking as fresh-faced and quick to smile as ever.
She's a morning person, she says, and indeed, she was up at 8am to supervise the building of a path to the house she shares with fellow actor Paul Blair. She's already been out shopping and before tonight's performance – 90 minutes of the most intense drama – she's squeezing in a quick voiceover for German supermarket Aldi.
It's not that she's glib about the play's serious content, it's just she'd rather not carry it home with her. "To be honest, we did laugh quite a lot in rehearsals," she says. "I think that's the nature of the material. You needed some kind of release. It's not been traumatic, but it's been interesting going into the bar afterwards and everybody ignores you. They don't know what to say. It's an amazing piece but it's really hard to watch."
There have, however, been points when even her cheerful faade has had to crack. Fortunately, having a boyfriend who understands the emotional strains of her profession means she has a shoulder to cry on.
"I did come home one night and have a right good old cry," she admits. "It was stress, but the material does get to you. The character is quite full on and when you've spent all day venting all this you need a release. The good thing about going out with Paul is he understands that; he's been there, done that."
What attracted her to the play was the challenge of dealing with its endless twists and turns. It is, she says, a gift of a part.
"The play's not about paedophilia, it's an illicit love story," she says. "I'm quite a romantic – which sounds ridiculous to say – but I do think there was definite love there. When you see them as adults, they've got a real connection and get on quite well. But the thing about the play is that you don't have an angle on it. As an audience member you're going with her, then him, then her again. It's definitely questioning me as an actor."
That Steele is on the stage at all is a sign of a performer willing to stretch herself. Many in her position, having gone straight from drama college into six series of a popular TV show, would never venture away from the comfort of the small screen.
Steele, however, is not only keen to take on roles in the theatre, but also to test herself in parts that challenge the cosy Sunday-night image of Lexie in Monarch of the Glen. She's given us gallus turns in John Byrne's stage version of Tutti Frutti and the revival of The Slab Boys; she made a fearsome wicked witch in the past season's Sleeping Beauty at the King's, Glasgow',; and now she's playing a woman who is riddled with complexity.
"Weirdly, when I left drama school, I went straight into television and you never think that's going to happen," she says. "That's why Monarch was so good for me because I got to learn so much, away up in the Highlands, with great people. But when I finished Sea of Souls it just seemed to be loads of theatre that was coming up and I've been doing theatre for the past two years.
"Everybody will always bring up Monarch, but it was nearly five years ago and things like Blackbird are so different. It's good to have that contrast. In this play I get thrown about the stage – my knee was bleeding last night and I'm covered in bruises. It's like being in a boxing ring. You haven't got a moment to think about it. It's just the two of us slugging it out. My body's so sore in the morning when I wake up.
"I always seem to be getting beaten up or having sex, but those are the meatier parts."
• Blackbird is at the Theatre Royal, Glasgow, 9-14 June.