Rising star John Heffernan is currently appearing in The Physicists at the Donmar Warehouse, which opens tonight (7 June 2012, previews from 31 May).

Since graduating Webber Douglas in 2005 he has notched up credits including Major Barbara, After the Dance and She Stoops to Conquer at the National Theatre, King Lear (with Ian McKellen) at the RSC and the title role in Richard II at the Tobacco Factory in Bristol.

Tell us about The Physicists
It’s a play written by a chap named Dürrenmatt in the early 60s. He’s a Swiss playwright and I have to admit I hadn’t come across him before. The only play I knew of his, from university, was The Visit but I didn’t know The Physicists at all. I think I’m right in saying that the only major production that it’s had before now was at the RSC in the 60s starring Irene Worth and Michael Hordern, directed by Peter Brook. It’s extraordinary, but it’s a weird play to describe. It’s a black comedy thriller, I suppose, but it’s somewhat amorphous. I watched Dr Strangelove recently and that’s the nearest thing I can compare it to in terms of tone. It was written in the shadow of the Cold War and examines that era’s threat of global annihilation while also laughing in the face of it – the absurdity of two countries wanting to destroy each other like that. But it’s probably best not to say too much because it’s constantly surprising.

And you play Johann Möbius
It’s all set in this insane asylum and he’s one of three inmates. The other two think they’re different people - one of them thinks he’s Newton and one of them thinks he’s Einstein. Möbius is a bit different. I hope it’s not confusing because there was actually a physicist called Möbius who pioneered something called the Möbius Strip, but Dürrenmatt only called him Möbius as a sort of tribute to him – he is an entirely fictional creation. Anyway, he’s been in this asylum for 12 years and been burrowing himself away working on his calculations and then things get blown out of the water quite quickly. He gets an unexpected visit from his wife and children who he’s never met before and then things spiral out of control from then on really.

Would it be fair to call Möbius a genius?
Well I guess parts of the play pivot on whether he is a genius or whether he’s a madman. The play posits the question that he could be the most intelligent man that has ever lived (no pressure!), and leaves Einstein and Newton in his wake. It’s about the burden of knowledge; how when you know everything you have to think about the consequences of that. And if the consequences are potentially damaging, maybe the best course of action is to keep it to yourself and not to share it.

Do you think this theme has a particular contemporary relevance?
I think so, very much. In fact I don’t think it’s a question that is ever going to go away – for example, I was watching the trailer for the new Ridley Scott film, Prometheus, and it seems to be posing a similar question. In fact, the figure of Prometheus is an interesting parallel with Möbius in terms of what you do with the gift of knowledge, and to what end you should use it. Whenever there is a scientific advancement that question keeps coming up. People keep saying, ‘is this going to be damaging? Where is this going to lead?’ And there is a lot of fear, I think, about progress and even using the word progress. So yes, it will always be relevant in that sense.

Attitudes towards nuclear warfare and energy have changed a lot since the play was written
We’ve tried to acknowledge that fact that nuclear energy has become something arguably very positive in the last few years. Harnessing that power has become a force for good as opposed to something massively destructive. But we have also been looking at the influence of terrorism and also at the freedom of information that comes with the internet. The idea of everything being out there for everyone to access. That question of censorship is also something which the play raises and that is very current now in light of Ai Weiwei, for example. Maybe the threat of nuclear annihilation has gone, but the lingering sense of threat is still there; it’s just gone off in different directions.

And attitudes towards mental illness have also changed significantly
Indeed - there’s something of the Cuckoo’s Nest about the play. It all comes back to the same idea: are the sane people really mad and the mad people really sane? I think it was Laing that started that sort of conversation but it’s something that the play picks up on, certainly – how best to treat mental illness. And it’s also about masks, people using madness as a defence mechanism and then you get the old Hamlet question: Are these people really mad or are they putting it on craftily?

How does it feel to be making your Donmar debut?
Terrifying, wonderful, exciting. It’s one of the sexiest places in London to work, isn’t it? The script came through my door a couple of months ago and you see that iconic Donmar lettering think,’wow’. It’s a very important season, particularly for Josie, but I’m trying not to think too much about the pressure. Obviously we want to do it as well as we can. It’s a great theatre and I’ve always been a fan. When I think about some of the amazing productions that I’ve seen there, to finally be performing in the space is a real thrill.

Sophie Thompson (Dr Mathilde von Zahnde) & John Heffernan (Mobius). Photo credit: Johan Persson

It’s funny that you’re coming from one of the biggest major theatres in London (the NT Olivier) to one of the smallest
I know! They couldn’t be more different. One of the first things I said in rehearsals was “Please make sure I’m not shouting every line!” So yes, it is a bit of a change, but I’ve been very lucky because I have not been on my own; Sophie Thompson was also in She Stoops to Conquer so has had to make the transition as well. We had our last performance of it on a Saturday night then had our first rehearsal here on the Monday morning so we were very much in at the deep end!

Are there any roles you’ve taken on since leaving drama school that stand out as particular highlights?
I was in a production of After the Dance at the NT about two years ago and that felt like a really special job. I think it was the combination of a play which not many people had heard of at all, and the fact we had such an absolutely superb company who could not have been lovelier or more extraordinarily talented. It was a very, very special time. Quite often when you reach the end of a run you think ‘well I’ve had a lovely time and it’s done now’, but After the Dance was one of those rare shows where you thought, ‘I wish we were doing this a bit longer.’ It was also that extraordinary moment Benedict (Cumberbatch) hit the big time - Sherlock came out in the middle of a run and he went from being someone who was obviously brilliant and very well respected to suddenly being this megastar. But more generally I feel very lucky in what I’ve had the chance to do and who I’ve had the chance to work with.

And which roles are on your wish list?
It’s hard to have dream parts in this business because it’s not in your gift really. I can genuinely say there is only one part where I’ve ever thought, ‘oh that would be really nice to have a go at one day’ and that is Richard II, who I was very lucky to get the chance to play last year at the Tobacco Factory.

A play that I think is fantastic which has not been done for a while is Edward II. It was done in Sheffield I think with Joseph Fiennes but it’s not been seen in London for a very long time. That would be great. And I’ve always wanted to play Constantine in The Seagull and Oswald in Ghosts, but in truth I’ll take what’s handed to me, I’m not very fussy!

I read an article recently where Mike Leigh said “there is no such thing as a career”, and I can see what he means. I’ve had conversations with agents who were saying, ‘I’d like to try and focus on this kind of job or that kind of job’, but in truth you are completely at the mercy of other people.

What prompted your interest in acting in the first place?
I became hooked on theatre through a series called Shakespeare - The Animated Tales which came out when I was about 11. The stories and the imagination of those short films completely fired me up and I was soon travelling to the Barbican every other Saturday to watch the RSC in action, and kept returning again and again to see incredible productions like King Lear with Robert Stephens and Adrian Noble's production of A Midsummer Night's Dream. It wasn't until I joined the drama society at Bristol University though that I started to get cast in plays and then I found myself really enjoying being part of a company.

If you could emulate anyone’s career whose would it be?
When I was growing up, I always loved watching Alex Jennings, who’s a bit of a hero of mine. And I suppose an actress like Miranda Raison (who's also in The Physicists), who is able to skip between different mediums, is a very good example to follow. Ditto people like Matthew Macfadyen and John Simm, who are able to do really great quality television. I realise that’s a pretty broad sweep but I’d happily follow in any of their footsteps.

- John Heffernan was speaking to Theo Bosanquet