In theory, what happened to Ben Whishaw two summers ago could happen to any actor. In practice, it was only ever going to happen to Whishaw. Trevor Nunn announced that he wanted to mount a new production of Hamlet at the theatrical citadel of the Old Vic, in which the lead role would be taken by a genuinely young man. It doesn’t require a leap of the imagination to picture the moment Whishaw showed up for the audition.

Though it’s impossible to think of him doing anything as strategic as dressing for the part, his advantage over other hopeful actors would have been clear before he even opened his mouth.

Just as everyone knows that God is the spit of Professor Dumbledore, in the end we all know what Hamlet is meant to look like, and it’s not Mel Gibson or Toby Stephens.

Hamlet has an unkempt mane of black hair, a lost look in his eye, a pallid complexion, a wiry frame — and he is, of course, draped from top to toe in black. In short, he looks exactly like Ben Whishaw. Then Nunn asked him to do the opening soliloquy: “O that this too too solid flesh...” His interest became apparent, recalls Whishaw, “when he asked me to do the speech again as if I were five years old or something. And I found myself getting very upset for some reason, then he seemed very interested”.

Two years on from his remarkable performance, Whishaw is still in black. Has he just not bothered to change? “It’s just actually today, really,” he insists. “It’s a bit of a rehearsal thing, and it’s a bit of a Konstantin thing.” It makes sense that Whishaw’s return to the theatre should involve the febrile son in Chekhov’s The Seagull. He stars in Katie Mitchell’s new production at the National alongside Juliet Stevenson as his mother, Madame Arkadina. In Whishaw’s slightly Eeyorish take on it, his casting as Konstantin makes almost too much sense.

“Most young actors do Hamlet, and they do Konstantin, don’t they? I did question whether it was the right thing to do, just because I think most actors live in fear of being typecast as something, and if you start typecasting yourself or putting yourself in a bracket, then that’s even more horrific.”

We shouldn’t take this anxiety too seriously. Questioning his motives seems to be a bit of a factory setting with Whishaw, because he also wonders whether he should have done Hamlet. “Retrospectively, I think, well, maybe it would have been good to have waited. I don’t think that if I were to do it again, I would do it in the same way. But it’s a ridiculous thought. It was wonderful for what it was.”

The Seagull is revived far less often than Hamlet, but when a new Chekhov does come along, two often turn up at once. The Royal Court was certainly rumoured to be planning a revival, while Nunn is directing the play at the RSC next year. It would have been bizarre if one of them hadn’t snapped up Whishaw. How similar are the two roles in practice? “They’re both sort of hypersensitive, depressed mummy’s boys,” he says. More than that, they’re both fatherless, both consumed by a slightly unhinged faith in the power of theatre and both very bad news for the young women they fall in love with.

Far more than Hamlet, the appeal of Konstantin for a young actor is presumably the craving for self-expression, even if it results in the risibly po-faced play he mounts for an unappreciative audience of family and friends. “Definitely it’s possible for an actor to make that leap of imagination,” says Whishaw. He mentions an exercise that Mitchell has used in the rehearsal room to help the actors find their characters. Dividing the themes of the play into unhappy love, family, the arts and destroyed dreams, she asked each cast member “to bring in a slice of your life that in some way illuminates one of those themes. So it’s very much your personal connection with the play”.

What did Whishaw bring to the rehearsal room? “I’m not going to go into unhappy love,” he says, only half joking. “What I chose to share with everyone was one of my first television filming experiences. I just had a naive picture of what actors would be like and what directors would do. I always thought that actors were other oddballs like me, they were all outsiders in some way. And, of course, they’re not. They’re the whole range of humankind. I remember finding that — and the fact that it’s a business, and there are other imperatives — was a destroyed dream, in a way, because it was a picture that shattered in my mind.” (He is not prepared to identify the culprit, but his television appearances have been as follows: one episode of Black Cab, Other People’s Children, The Booze Cruise and Chris Morris’s sitcom Nathan Barley. He confirms it’s not Nathan Barley.) You can’t fake that level of sensitivity, which is why he was such a convincing Hamlet, and one reason he landed the lead role in Perfume, the long-awaited cinematic adaptation of Patrick Süskind’s novel set in the stink of 18th-century Paris. Whishaw plays Jean-Baptiste Grenouille, whose sensitivity is all olfactory. Giving off no personal aroma of his own, the character embarks on an increasingly unethical, not to mention murderous, hunt for the perfect scent.

The actor clearly had a similar impact on the director Tom Tykwer, best known for Run Lola Run, as on Nunn. “I auditioned for it just after Hamlet had finished, and they wanted to go with it in the winter of that year. They were banking on the director enlisting a big star to do it. Because, suddenly, the director decided he wanted some unknown guy from England, it kind of delayed the whole thing.”

Whishaw knew of the book “through friends, who told me I had to read it because it was amazing”. Those friends may not recognise in his performance the physical manifestation of Grenouille’s moral hideousness. “There are some quite big changes, just in terms of the whole tone of the piece. Maybe they’re good, maybe they’re not. I don’t know.

There were so many questions about how you try to make that character accessible to an audience. In the book, he’s a hunchback with a gammy leg. We’ve gone for something a bit more neutral.”