Multi-award-winning playwright Simon Stephens is a pale giant, dressed today in dark blue jeans, a maroon shirt and a charcoal grey jacket. He listens and laughs a lot.

Simon Stephens © Alex Rumford

We’re sitting upstairs in a quiet corner of Black’s, a members’ club in London. The setting is intimate and our talk about his new play, Heisenberg: The Uncertainty Principle is too. The blurb for the show reads: ‘When two strangers meet by chance amidst the bustle of a crowded London train station; their lives change forever’. The play receives its UK premiere at Wyndham’s next month and tells the story of two strangers who strike up an unlikely relationship. It stars Anne-Marie Duff and Kenneth Cranham, and reunites the production team behind The Curious Incident of the Dog in the Night-Time, with Stephens, Marianne Elliott and designer Bunny Christie. “Ken and Ann-Marie have a very complimentary energy that’s absolutely perfect for this play. Ken has such earth and a stillness and Ann-Marie has an edge and desire. The two of them dance around one another and it’s kind of exquisite,” he says.

The play is directed by Marianne Elliott and is the inaugural show for Elliott & Harper Productions, the company she has set up with director Chris Harper. Elliott’s many credits include Curious Incident (adapted for the stage by Stephens), War Horse and Angels in America. “I hope it sells – for them,” says Stephens, “I don’t want them to be exposed to anything. I really love them. If I’m anxious about anything, I’m anxious about the people of that calibre enjoying the success that they deserve.”

Is he nervous? “I’m really happy. I’m not nervous. Because the play has been done before in New York,” Stephens replies. “When a play is being done for the first time your main fear is that it is shit. I kind of know that it’s not shit. It’s not a shit play. There is something about bringing Heisenberg to London which means a lot to me. A lot of my plays are carved out of a love for this city.”

We talk about his friendship with Marianne and I get a clear sense of how and why they work so well together (Simon is Godfather to her daughter and it was some time into working together that she and Stephens discovered that they were both from Stockport and that they used to get the same bus to their schools.)

Simon Stephens and Marianne Elliott © Alex Rumford

“She’s brilliant because she’s brilliant – we have a brilliant relationship because of some deep psychic connection,” he says. “Above all of those things, she’s the hardest-working director I know.” Hard-working in a different way, he explains, from Ivo van Hove and Sean Holmes, say, who run theatres or do show after show, back-to-back in Paris or on Broadway. “Marianne refuses to go back-to-back with shows. Stephens continues. “At a time when everyone wants her, she says no to so many jobs because she needs the preparation time. I don’t know any director who prepares more than her. Heisenberg is an hour and fifteen two-hander and she has six weeks preparing it so that when she talks to the cast at the beginning of rehearsals, she speaks with more depth about the play than I have. What she’ll bring is the sense of its existential depth.”

He’s on a roll about his peers. “I’m so fucking fortunate, Carl. I’ve been so fortunate with the collaborators that I’ve worked with. Really lucky,” he says, thinking. “To work with Sean Holmes again and again, a substantial ten-year relationship. A fifteen-year relationship with Sarah Frankcom as well as the rockstar directors like Katie Mitchell, Ivo van Hove and Sebastian Nübling… It’s completely thrilling.”

There’s nothing smug about the way Simon Stephens says that, just a thankful recognition that he has done incredibly well.

I say I think his writing is often desolate but never without heart. In these uncertain times, how important is optimism? “I think Heisenberg is infused with the possibility of optimism and I think that is important. The only response to a world in peril is to be optimistic – I think pessimism is the last resort of the privileged,” he says, tucking into his artichoke soup.

“There is a difference between optimism and naivety – between optimism and jolliness. Real optimism has to consider real peril, real despair, real fear and real isolation. To deny those is just naïve but it’s about acknowledging those and finding the determination to persist.”

Rather brilliantly, there are 30,000 tickets for Heisenberg available for under £20. Delivering work to audiences at an affordable price is important to Stephens. “I’ve been a teacher all my life,” he nods. “There is nothing more important to me than the notion that theatre is not an elitist art form but that it is a democratic art form. You can make it cheaper than a lot of cinemas. You can make it cheaper than a football match. This is like watching a Champion League Football match at the cost of watching a match in the Ryman Conference.”

Heisenberg isn’t the only play keeping him occupied. Stephens’ adaptation of Chekhov’s The Seagull opens at the Lyric Hammersmith the day after and he has come from rehearsals to meet me. “I’m more nervous, weirdly, about The Seagull,” he admits. “I really like writing versions – it’s thrilling for me. It’s simple, it doesn’t take a massive amount of time and it’s different from play to play to play. 10 years ago, when I was working on Harper Regan and Lesley Sharp asked me to write a version of The Seagull, I knew I wasn’t able to at that time in my career. Because in my opinion, Chekhov is the best writer in the history of the world. For me, he is my tower. Do you know the Leonard Cohen song ‘Tower of Song’?” he asks.

I tell him I don’t.

“It’s a really beautiful, beautiful song. In it Cohen sings about the Tower of Song – a tower that all songwriters live in and there’s a beautiful line about Hank Williams.” Stephens quotes: “‘I said to Hank Williams: “How lonely does it get?” Hank Williams hasn’t answered yet. But I hear him laughing all night long. Oh, a hundred floors above me in the Tower of Song’.”

He continues, “I think writers position themselves at the foot of towers and they are very specific about which towers they position themselves at the foot of. I’m sitting on ground floor of Chekhov’s Tower and he’s a hundred floors above me, laughing all night long,”

It would be easy to pin him down as a tortured artist. How does he manage ego? “I find it really confusing because there’s part of me that still thinks I’m desperately trying to hack away, trying to get it right. As I look at my career now, objectively – if I separate myself from the experience of my career – I think you’d look at it and say that it is probably the career of a successful playwright. But I don’t experience myself as being a successful playwright,” he admits, modestly.

“I think the only thing you can do is, you stay present tense and concern yourself with the work and just get the work right. This is not just for successful playwrights, I think it’s true of all playwrights,” he continues. “I think it’s actually more perilous for writers at the start of their career because they are so worried about career that they can stop worrying about the work. I can’t change anything… It took me about 10 years to get over the notion of linear improvement. All I really want to do is write a play that is different to the last one. If ever it comes close to me taking myself too seriously then my children and my wife will just take the piss out of me – so brilliantly and precisely that it’s just impossible.”

I shift the conversation to critics, specifically, Michael Billington, who we both agree gets a lot of stick from the blogosphere. “If you’re working in theatre and you can’t distinguish between Michael Billington and Quentin Letts say- or Michael Billington and Dominic Cavendish, then you’re a fucking idiot,” he says, smiling. “If you can’t acknowledge that Michael Billington is one of the most consistently thoughtful, economic, searching, knowledgeable and serious writers about theatre.”

Stephens is Artistic Associate at the Lyric Theatre and Associate Playwright at the Royal Court. Does he think there are issues with the way new work is being commissioned that need addressing in order for the next generation of playwrights to break through? “I think there are perhaps some structural issues. But the structural issues are really complicated,” he says.

“I’m old enough to remember the year 2000 and the early years of the Blair government – and the remarkable energy for the arts that that government had and the extraordinary investment that that government brought about,” he explains. “I forget the name of the report in 2000 celebrating the agency of new writing and instigating a cash injection into new writing. But within five or ten years there were more playwrights than there had ever been and they were funded and supported. There new writing groups and young writing schemes all over the country. Eight years later there was an economic collapse that we’re still reeling from and the consequences of that is a massive withdrawal of money from the arts.”

“So, we have this situation where there are four times as many playwrights and less money to inject into the productions of their plays. That’s really tricky for the well-intentioned artistic directors who have to let people down. They will, and have rejected major significant playwrights and that’s an ongoing thing. I don’t know what to do about it because we are unfortunately not governed by a government that believes in the arts. The nature of Conservatism is that it has an impulse to conserve and the one thing the arts are not interested in ever – or should never be interested in –  is conserving,” says Stephens.

“Julian Fellowes is the only playwright in the world who has any vested interest in things staying the way that they are and that’s why he is a…”

Just in time his phone beeps. “That’s my timer,” he sighs. “I need to be thinking about making a move.” Another rehearsal to get to?

No, he laughs, and heads off down Dean Street to pick up his daughter from school.

Heisenberg: The Uncertainty Principle runs at Wyndham’s Theatre from 9 October to 6 January, with previews from 3 October.

The Seagull will run at the Lyric Hammersmith from 10 October to 4 November, with previews from 3 October.