His lisp cannot easily be transliterated. The letter ‘R’ starts somewhere at the back of his throat and stays there. Words containing the letter are, therefore, afflicted with a strange hiatus, an unresolved gurgle. The effect is dandyish and childish at the same time: a paradox, in fact. One of many.

‘I want it to be as inaccurate [this comes out roughly as ‘inaccuchywate’] as possible,’ he wrote to Ira Nadel, Professor of English at the University of British Columbia. Nadel had asked Stoppard if he would co-operate with a biography he was writing. No, Stoppard would not. Nevertheless, Double Act: A Life of Tom Stoppard (Methuen, £25) has just been published. Its 621 pages are lying – brick-like, inert – between us on a table in the chairman’s office in the National Theatre.

‘No, I haven’t read it. I noticed that quote about inaccuracy in a brochure they sent me. It’s perfectly accurate. The idea of having a book about me I find just appalling. I just didn’t want it. Methuen sent me a copy and I saw the photograph of me and my big brother and my mother’s passport. I mean what has that got to do with me? I really resented it.

‘I told Nadel that I wasn’t going to tell anybody not to speak to him. I wish I’d said don’t give him any baby photographs. He’s a perfectly nice guy. I had a drink with him in San Francisco. He’s worked for a long time on that book. I can’t resent it because he’s worked very hard, but I’ve got no curiosity about it and I’ll never read it. There are I don’t know how many books about my plays and I’ll never read any of them. He says it’s just a literary book, but it’s clearly more personal than the other ones.’

But, I wonder, doesn’t the biography echo the fact that he has, lately, grown more interested in his past.

‘I haven’t been indifferent to it previously. But I have found out more about my antecedents in the last ten years. The fact that I discovered that I am Jewish has been overstated. I knew perfectly well there was some Jewishness in me, otherwise the family could cheerfully have stayed in Czechoslovakia through the war. And I remember my mother saying to me that if you had one Jewish grandparent you were in trouble. She didn’t tell me that all my grandparents were Jewish and that she had sisters who were killed by the Nazis.

‘My mother had this weird idea that when we came to England as little boys we’d be discriminated against if it was known. She just thought we should draw a line and start again. She was wrong. I was never aware at school or at my first job of boys being noticed as Jewish. My mother was nervous but she had no cause to be. My stepfather married a Jewess with two children, which is very strange because he was a bit anti-Semitic. But anti-Semitism is not something I’ve ever experienced – except, of course, when I was eighteen months old.

‘It was a deep shock when I found it all out. That she never told me was as much a shock as the fact itself. But I don’t suddenly feel more Jewish. I don’t want to go and live in Israel.’

But there is, in Stoppard, an abiding interest in the biographies of other people.

‘All through my adult life I have been brought to an interest in a particular writer’s work by reading a biography. It makes a large difference to me where a writer was or what was in his life when he wrote this.’

In fact, his play Travesties was a prolonged joke about biographies – notably the coincidence that brought Lenin, James Joyce and Tristan Tzara together in Zurich during the First World War.

‘It was like a joke about biography. It was a tale told by a senile amnesiac.’

Henry Carr, the hero of Travesties, looks down on artists as hopelessly disengaged but absurdly lucky people. He is partially modelled on Stoppard’s stepfather. Stoppard is aware of the charge of being privileged and politically irresponsible.

‘I’ve always been aware of potential criticisms coming from that direction. Being brought up in the kind of family I was. They never went to theatres, concerts, art galleries. I was aware of becoming the kind of person of whom one might say, “Why doesn’t he get a proper job?”’

His new play at the National, The Coast of Utopia, is a trilogy – Voyage, Shipwreck, Salvage – set in the political ferment of mid nineteenth-century Russia.

‘As the title implies, it’s about people looking for and discussing the ideal society. It’s political philosophy as drama. But the political philosophy is only one aspect of it. It’s the only play I’ve ever written with so much domestic small talk in it. This is going to sound like jargon, but there’s a micro-narrative and a macro-narrative. I’d always been fascinated by the micro-narrative in Chekhov and I always thought I’d like to try and write something like that. There are large subterranean movements going on in relationships between characters, but they are conveyed as though they were clues which you have to pick up. That really attracted me.’

Stoppard is almost unique among modern British writers in that he is driven by ideas. Indeed, the most consistent criticism of his plays is that they are about ideas rather than people. But he can’t help it. He is always initially gripped by an idea.

‘They are indeed what’s driven me to write almost everything. I’ve very rarely been stimulated to write a play by a particular situation or joke. It’s the idea which is the play. It’s almost a secondary stage to look at a set of situations and characters through which to convey the idea. I don’t ask myself why. I don’t even know there’s an answer I could dig up from myself. “Why not?” seems to be a good answer.’

Perhaps the truth is something to do with the fact that he never went to university. ‘I suspect I did have a natural affinity for the academic life. I think the plays I write are a kind of displacement. I didn’t flower at school, it was just an experience I had to get through. It put me off extending my education to university. I couldn’t wait to get out. I often write nowadays as a sort of self-education, to replace the education that I never received. It grew out of purely personal desire to know things. It wasn’t a duty, it was self-expression of some kind. I have felt ever since that I’ve been trying to catch up on those four or five years when I wouldn’t have had to earn a living.’

One result of this catching up is that he over-researches everything. The Coast of Utopia is a trilogy because his material overflowed into three plays.

‘Research is not a duty, it’s something I relish. I suffer from a comprehensiveness neurosis – if that is a medical condition you can have. I over-prepare. Perhaps it’s the kind of self-education which has a lack of confidence behind it.’

But it does mean that his plays are not just games for the layman. Jumpers dealt thoroughly with philosophy. Hapgood betrayed a deep understanding of quantum theory. Arcadia was steeped in chaos theory – notably in the image of the rice pudding. If you put jam in a rice pudding and stir, it first forms spirals and then turns completely pink. But it does not recover its original condition if you stir in the opposite direction. It is a perfectly Stoppardian paradox.

‘It appeals to the fantasy and imagination and poetry in oneself rather than the science. If you stir a bowl of sugar and sand long enough, there ought to be a moment when the sugar and the sand are completely separate. It is an idea potent with metaphor and fantasy.’

Typically, this thought segues into a consideration of the technicalities of writing plays. Specifically, it makes him think of the difficulty of blending ideas and life.

‘I think the difficulty with this sort of play is to get the sand and sugar mixed – the personal narrative with the play of ideas. I don’t think I have ever really succeeded. I think there’s always a point in these plays when you admit to yourself that you’re going to make this point and it happens to be in the kitchen when somebody is washing up or in the bedroom when somebody is getting ready for bed. You try to make it all part of the washing up or whatever but actually it’s just stopped. You have to say: turn off the taps, stop messing with the pillows and listen to this. If you don’t overplay it, that’s okay. But there is a Platonic play or perhaps a Chekhovian play in which all these ideas are developed and completely clear.

‘But I accept the limitation even though I am aware in the weave of theatricality it is a kind of interruption

‘But I can’t conceive of a play that would be an interesting couple of hours in the theatre where two people are debating something and nothing actually happens. It would be an improvement on a real debate in certain senses. It would all be rewritten and compressed until it was fairly clear.’

I mention Samuel Beckett’s Three Dialogues with Georges Duthuit, which, startlingly, he hasn’t read. He is embarrassed by this, particularly since he has a first edition of Beckett’s Proust in which the dialogues appear. But he is entranced by the mention of Beckett.

‘I am reading Malone Dies as bedtime reading at the moment. I keep laughing out loud. I can see why it appeals intensely to some people and means nothing to a lot of people. It’s a strange marriage between close study and imaginative writing. The jokes only emerge from careful attention. Beckett interrupts himself but he doesn’t give any typographical clue that that is what he is doing.’

I draw him back to The Coast of Utopia. He wanted to do something Russian.

‘I was trying to write about Belinsky, Herzen and Bakunin. The family life at the Bakunins suggested the sort of thing I wanted to write about – birch trees, drinking tea out of glasses and talking . . . There was also Turgenev with A Month in the Country, and Summerfolk, which I saw here and thought, “God, I’d like to do one of those on this set.” The Russians are very interesting to a dramatist – though one mustn’t generalise about nationalities – but it’s the volatility of the emotions in Chekhov. There’s this melodramatic emotionalism followed by cheerful laughter or whatever. They couldn’t be English people, it’s just not the same.

‘I seem to have read more Russian writing in the past five years than I did in the previous twenty-five. There’s less separation in Russian literature between the artistic and social drive of the work, the book as a social fact and as a fact of art.’

He speaks of a Russian literary critic who had the high-aesthete view of art of a Parisian dandy, in spite of the social turmoil around him.

‘In point of fact he never came to understand social realism because he died young. But he did end up understanding that, if there’s a fire in the street, you run to the fire and do what you can, otherwise what kind of neighbour are you? you didn’t write a poem about the flames even if it was to be the best description of flames in the language.’

I remember an odd point that came up in the biography. Stoppard’s favourite line in a film, claimed Nadel, was in The Fugitive. Harrison Ford, found guilty of killing his wife but escaped from custody, confronts Tommy Lee Jones as the US Marshal trying to catch him. Ford says, ‘I didn’t kill my wife.’Jones replies: ‘I don’t care.’ I mention this is also one of my favourite lines. Stoppard slaps me on the knee.

‘Then we understand each other and there is no more to be said.’

I gesture at the tape recorder.

‘Okay, it was a perfect moment. It subverted the whole film industry, the entire convention trembled at that point. Also Harrison is probably getting paid ten times as much as Tommy Lee Jones and he says, “I don’t care.” It’s wonderfll.’

Stoppard is once more working on films. He’s writing a script for Tulip Fever and looking forward to writing the screenplays for the Pullman trilogy. The striking thing, I remark, about his screenplays – like Shakespeare in Love – is that, good as they are, they are not Stoppard plays.

‘No, they’re not. I don’t have an investment in films personally. The film isn’t there to carry an idea of mine. I haven’t invented the characters. In Shakespeare in Love I was working from a screenplay, in every other case I’ve been working from a novel. So I’m given characters and narratives and ideas. It’s an interesting, complicated and technical job.

‘Of course, you can’t completely suppress your own contribution. You do bring something but that’s all relative to the fact that you have inherited the whole caboodle and you’re going to deliver it to somebody who is going to direct the screenplay that he or she wishes to direct. For that reason I don’t think of screenwriting as a continuation of my life as a writer. It’s a separate track. It’s not a problem unless you go in with the wrong attitude, namely that they are all there to do your film. And my real writing life is what happens here.’

He is also aware that there are certain great film effects which he cannot write. One of his favourite moments in cinema is in Roman Polanski’s Chinatown. There is a shot of a house which appears to be a still, but then some smoke drifts across the shot and you realise Jack Nicholson is just outside the frame.

‘I’ve never written an instant like that in a screenplay. I’m always thinking about what people say to each other. The idea of the story being conveyed in pure cinema terms is not something that comes naturally to me.’

A curiously Stoppardian announcement has been coming over the tannoy in the office – ‘This is a test page.’ ‘A test page!’ he exclaims, ‘What the fuck’s that?’

If a writer’s name alone both evokes another world and changes this one, then he is probably great. Stoppard does both. Everything in his immediate vicinity tends to become Stoppardian. The Chairman’s office looks like a stage set for an Eighties drama that could be one of Stoppard’s plays within a play. The cigarettes he elegantly chain-smokes, even though they are very light Silk Cuts, balance dandyism and death. The alarmingly youthful look – the hair is still a wonder – suggests Dorian Gray, which suggests Wilde, who, of course, suggests Stoppard. The strange combination of amiability and reticence that could be bafflement, all wrapped in an awareness of biting interstellar cold – this is Stoppard. And the lisp. It could be nobody else.