Mike Nichols sits at the table sipping chicken-noodle soup and crunching on pickles so loudly he feels the need to apologise.

The man who fired the sexual fantasies of a generation is now 73, but he remains as intrigued by lust as he was nearly 40 years ago, when he created the cinematic image that defined a decade - the sight of Mrs Robinson rolling a stocking down a never-ending leg to seduce her daughter's date, Dustin Hoffman, in a motel bedroom.

Sex, infidelity, marriage, truth and lies are still on the menu. In his latest film, Closer, he's still questioning the nature of love and the mystery of desire, holding a mirror up to the emotional complexity of relationships in which sex is too easily assumed a visa to validation.

It is a rainy November afternoon in an enormous rehearsal studio in the heart of Times Square in Manhattan. Behind a ballet barre are floor-to-ceiling mirrors. Nichols has taken a break for lunch; he's rehearsing his latest project - directing Spamalot, a musical stage version of Monty Python and the Holy Grail - but stage comedy and his love of British humour must wait. He wants to hold up a mirror to the relationships between men and women, and in doing so he holds it up to himself too. He explored the theme in The Graduate and again with Jack Nicholson in 1971, when he made Carnal Knowledge, and feels the time has come to revisit it.

"It's very interesting what changes in relationships with different generations. Masochism, for instance. People my age, if you show them Brief Encounter, they weep and identify. If you show Brief Encounter to [young] people now, they say, 'What's wrong with them?' Denying yourself and saying, 'We mustn't do this, we can't' - that's all over. That kind of back-street masochism - it's all changed."

We sit at a Formica table across from a vacant piano, dwarfed against the wall of mirrors - an invitation to distraction and vanity - but so far he hasn't checked himself out, which suggests a man who's either very content with himself or consumed by his subject. Minutes earlier, an assistant had delivered chicken sandwiches, pickles and soup from the deli downstairs. Now, between crunches that echo in the emptiness of the rehearsal room, he dances from deceit to fidelity to secrecy.

"No one can say, 'You must tell me' or 'I have the right to know.' There is no right to know anything. What's in people's heads and what they've done in their lives - including last night - is their business. I think that if you trust someone, you don't look through his or her drawers. You can only hope. You don't have a right to it. Here's how I feel about it. You can offer fidelity. You can't ask for it."

Nichols is half of one of America's most celebrated couples. He has been married for the past 17 years to the broadcaster Diane Sawyer. They are the dinner-party guests everyone wants but are unlikely to get. Partly because he dislikes parties, but mainly because he adores his wife and, on the simplest level, it's made him less interested in leaving home.

"I think that there is such a thing as finding the person for you and that not only is that enough, but the life you make together, which includes everything, only increases the commitment to each other - because you want to. So you literally forget what parties are for. When you're young, they're about meeting people. And when you're no longer concerned about meeting people, you can forget the point of them.

"Staying home becomes the rare treat. Especially if you work a lot. We work a lot, so nothing is more exciting and glamorous than an evening where we have nothing to do."

For more than four decades, Nichols (with Who's Afraid of Virginia Woolf?, The Graduate, Silkwood, Carnal Knowledge) has been in the pantheon of great American directors. His deft touch and ability to extract humour and absurdity from the ordinary extends beyond directing movies. He has won a record seven Tony awards for Best Direction on Broadway (including Tom Stoppard's The Real Thing), and in September he looked seriously uncomfortable as he stood on stage at the Emmy awards, receiving a standing ovation from America's elite, Al Pacino and Meryl Streep included, for directing Tony Kushner's Pulitzer-prize-winning play, Angels in America.

As a film director, he has been a pioneer. He is known for his long opening shots, most notably Dustin Hoffman on the moving walkway in The Graduate, which Quentin Tarantino paid homage to with Pam Grier in the opening of Jackie Brown. He is admired, too, for his bold casting choices. In particular, choosing Hoffman as Benjamin Braddock. The character was written as a Wasp athlete, tall and blond, and in casting the then-unknown Hoffman in his first film role, he redefined the criteria for a leading man.

Nichols speculates that North Americans' perspective on adultery shifted after the war. Mass transport, the empowerment of women and the redefinition of sex as an urge for intimacy, rather than just a contract for procreation, moved the goalposts. "Back then, a married man could reasonably expect a woman to live out of sight if he had a mistress. To give up her life to waiting for him. It's harder now to find people to play that game.

"It's easier in Europe. There are far more marriages there that are openly an arrangement than there are here. I know so many European couples where neither has been faithful year after year after year, and then strangely, when one of them dies, the other one is devastated, finished - it's the end. Because it was really love. But they define it differently. It's harder for us [in the US]. We believe in fidelity even if we can't achieve it."

His new movie, Closer, is based on the award-winning play by Patrick Marber, who has also written the screenplay. Adultery is a fascinating topic and one that is explored with scrupulous honesty in the film. It is a study of modern relationships and it's not surprising that Nichols was drawn to the material. Like Carnal Knowledge, it examines the nature of casual betrayal, intense attraction, and the uncertainty of love and sex. The four characters (two couples played by Jude Law, Julia Roberts, Clive Owen and Natalie Portman) are wounded and at times unlikable, but always relatable-to, in spite of - and often because of - the lies that they tell. "My wife said that it was about how people have to remember the importance of lying in love. You have to be willing to lie sometimes." The very nature and degree of deceit is what intrigues Nichols.

"It's an infinitely complicated and insoluble subject, because there are as many variations as there are couples. Feelings can be more of a betrayal than acts. And what do you say about that? 'I never touched X, but I had certain feelings for them?' It's all about what people have promised each other. But two people hear different things, and that's where the trouble starts." He raises a quizzical eyebrow.

"Over and over, people tell me things about their mate and I'm always stunned. I think, don't you know that's the beginning of separating? That if you tell somebody outside anything at all about the person you love, that it's the beginning of the end? You can't. Lots of people don't know that, so what is betrayal? Is it talking at all to anyone about the person you love? I'd say so."

Sawyer is Nichols's fourth wife. From his second marriage, to Margo Callas, he has a daughter, Daisy, and from his third, to Annabel Davis-Goff, the Anglo-Irish novelist, he has two other children: Max and Jenny.

What's intriguing is that, while Closer deals with the uncontrollable narrative of love, Nichols himself still believes there is such a thing as finding the one person who is enough, but admits he didn't discover this until middle age. For him, this person was Sawyer, whom he met while waiting to board Concorde. When he speaks of their relationship, he is very matter-of-fact, as though it's the only absolute in his universe of questions. "It felt as though I met the person I was meant for. That all the weird things about you finally seem to have a purpose. As though they were waiting for this particular conjunction. And then everything is different."

Nichols was 35 years old when he received his first Academy Award nomination for Best Director for Edward Albee's Who's Afraid of Virginia Woolf? He didn't win but Elizabeth Taylor took home Best Actress. Richard Burton had said about his directing: "He conspires with you to get your best."

He won the following year, in 1967, for The Graduate. He was subsequently nominated again for Silkwood and Working Girl, and shared a nomination for Best Picture for James Ivory's The Remains of the Day, on which he was producer. But unlike today, where the American dream is no longer to be president but to direct, in the late 1960s his early success was considered a phenomenon. "People have an opinion of something you've done. And they assume you have a high opinion of it. But mostly you agree with them."

Is he hinting at dissatisfaction, so often the by-product of the truly creative mind?

He clarifies: "If someone says that was a crappy take to do, you can't go through life saying, 'Oh yeah, wasn't it? It was disgusting. I hate myself for that.' But that is what you're thinking a lot of the time. I'm not proud of that."

In Closer, given the nature of the subject matter and the rawness of the feelings it explores, his job, he feels, is to scratch away the surface and get to the core. The film took nine weeks to shoot in London, and he presents the city lovingly, glistening with light in the most magical way. About this he says: "I didn't want them to look dead. There just isn't a lot of sun."

He has lived in London on and off, but never for very long. "I lived there many years ago.

I think I was with somebody who had a house there. And, mysteriously, Maggie Smith lived with us. I'm not sure why." He also lived there when he made Wit (for HBO), starring Emma Thompson.

His affection for the British sensibility is obvious. It extends back to the earlier days when he was with his former comedy partner, Elaine May. They were revered for having launched the 1960s satire movement in the US. "We followed Beyond the Fringe and we were friends with all the guys. Peter Cook was a friend, Dudley Moore was a friend. I've always loved them. And Python. I've been friends with the Pythons for most of my life. Eric [Idle] and I have been friends for 25 years."

In 1960, the show An Evening with Mike Nichols and Elaine May ran on Broadway for a year. Then, despite its immense popularity, they decided to split and pursue separate careers. In 1966, Nichols appeared at London's National Theatre in Wallace Shawn's The Designated Mourner. But performing is not something he misses: "I'd rather be a daddy than a baby."

When it comes to British humour, his appreciation is boundless; he cites its quality as insulting without being offensive. "It goes back so far - uninterrupted. Ours is interrupted. There is a big break after vaudeville, before television. There was another big break after Jack Benny. It kept getting broken off and starting again in America, whereas in England it was continuous. It's also very much a part of everyone's life [but] here it's more specialised. Here, some people love comedy, some people don't."

Nichols has kept abreast of British comedy and applauds Ali G. "He has really invented a new kind of comedy. It's the comedy of real people tested in various ways. Not like a reality show where people eat bugs, but by being presented with unexpected stereotypes and clich_s." Nichols acknowledges that in Britain you are allowed to have a point of view and it is not considered rude.

"Look at them in parliament. It's a wonderful thing: true debate. There are many English conventions that would be very useful to us. That's one. The idea of a real debate. Not a rigged debate. Another is self-deprecation, which is highly cultivated by English people. Even people who you don't think have the soul of democracy, like Prince Philip - even he has learnt self-deprecation. It's the first thing you get when you're a kid. We don't have that. To put it mildly.

"I think that somehow, somewhere, we got piety and earnestness mixed up. And because we're such a big country for talking about religion as well as practising it, it's become a little bit of a club. Not a club of people banding together but something to club people with. 'This is how I worship. How do you worship? I worship better than you do because I believe better things. My God is better than your God.' And all humour is out the window as soon as you start that stuff."

He finishes the soup and moves on to the sandwich. "The two things I dread most are earnestness and piety. They're a blight.

You have to recognise a reality or you wouldn't laugh; therefore a laugh is the enemy of earnestness and piousness of any kind. And I just think they have more experience with all that in Europe. They don't bludgeon people with their beliefs in the same way."

Self-deprecation is also a way to diffuse anger, which leads Nichols to a discussion about anger being the fuel of humour. "There are people who can be funny without being harmful to anyone, but that takes great lightness on your feet and sophistication. By and large, I think funny people are angry people."

The comment is a rare glimpse at his self-portrait. He sees himself, for all his humour and interest in relationships, as an angry person too. "But I'm angry about things that I don't even remember any more, it was so long ago. So I have a reflex of anger."

For instance, whenever he enters a crowded party or event, he says his wife knows to stick very close to his side - especially with the first three or four people he encounters. "She has to laugh a lot, so the people I attack think it's a joke. And then explain that I get in a certain state when there are a lot of people and that I get aggressive, which is really defensive, which goes back to grammar school."

Some of this is grounded in being a refugee, coming to a new country, and having a lonely and isolated childhood. Born in 1931 in Berlin as Michael Igor Peschkowsky, a German-Russian Jew, he arrived in New York at the age of seven, bald and devoid of body hair due to an adverse reaction to a whooping-cough vaccine given when he was four. To escape the Nazis, he and his younger brother, Robert, made the journey alone from Hamburg. Mike arrived knowing only two sentences: "I do not speak English" and "Please do not kiss me." His father, Paul, a doctor who had fled to Germany after the 1917 revolution in Russia, then fled Germany for America, was waiting for them. His mother, Brigitte, joined them a year and a half later, having been ill. Nichols learnt at a very early age to be alert and mistrust people. His father died when he was 12, leaving his mother, 34 and with no profession, struggling. Going to school, not speaking the language, hairless and wearing a cap, Nichols developed his intellect and keen observational eye as a suit of armour. Humour was the antagonist of self-pity. "Being an outsider, being tested and mistrusted as an outsider, and whatever it is that helps me know about people when I'm making a picture, is also the same thing that lets me know what everybody's thinking all the time. Which is not very pleasant. I don't want to know what everybody's thinking."

School was not an enjoyable experience.

He went to various progressive private schools, including a boarding school in Connecticut where he was taunted and bullied. He attended the University of Chicago, which is where he met Elaine May and began doing comedy.

He worked his way through college, taking jobs such as night janitor, classical DJ, and post-office truck driver. The last was a struggle, as he was no good at finding addresses.

The imprint of being a refugee left him with acute powers of perception. He was trained to pick up on phoniness. But are his perceptions always accurate? "After a while. Not to begin with because I'm so - what's the word? - touchy to begin with. I don't trust people. But I've learnt that if you don't move towards generosity, you die. You can't live like that. And there's a reason to trust many people. I have to fight my reflexes and I'm getting better."

Betrayal, when stemming from childhood, results in an expectation that betrayals will occur again and again, so a person is constantly anticipating them. Nichols hypothesises that children are socialised to accept it, so tolerance is built up. "It's funny how early it starts in life. You're in your stroller and this huge, fat lady says, 'Aww, coochie-coochie-coo.'

You turn away, because she's noisy and she's pinching you and she's scaring you. And your mother - your own mother, who would die for you - says to her, 'Oh, he's just really shy with strangers.' And you're left there thinking, 'Are you nuts? You're taking this stranger's side against me? You're making comments about me to a stranger? You must be out of your mind.'" He smiles.

If there was anything he could change about himself, he says, he'd like to be able to count on being able to be kind all the time, not just some of the time. "That's the biggest change: that I'm able to control my behaviour enough so I'm never unkind. It's a constant battle with me."

He gives a perfect example by comparing his instincts with those of his wife: "If you wake me up in the middle of the night, I shout, 'What?! What do you want!?' If you wake her up in the middle of the night, she'll say, 'Are you all right?'"

But after so many years of building defences, is it possible to change? "It's possible to improve. To keep setting the task of being less of an asshole. It's like exercise. My kids used to be embarrassed by my irritability. They've said to me that they're proud of me because I've gotten so much better, and I'm pleased. I don't want them to be ashamed of me. It's hard work if you're an irritable person. I have to keep remembering. Because I started out a prick. So I have a lot of work to do." He laughs.

Before he leaves, there is one last topic to explore. It is noteworthy that he has deliberately made a film that is about the dynamics of sex but which has no sex scene. True, there was no sex scene in the play, but when did that stop a director from changing the story? He leans back in the chair.

"Do you remember in Lolita, as soon as he gets her, there's no pleasure again - ever. Ever. For either one of them? It's not about sex. It's about the ancillary things that come with sex.

"It's like what I always say about sex in a play. Sex in a play is like that scene in The Meaning of Life, where John Cleese is with his wife, and the teacher's demonstrating sex for the classroom - it's like a demonstration. It's like watching people eat. You're so essentially left out of it that you might as well not do it."He ruminates that sex today is all spectacle. For instance, women with fake breasts. "Who are they for? They know and the guys they're with know. So are they for people who walk by on the street?

I never understood it.

"Unless it's about seeming to be something. And that's where we're in the biggest trouble. Everything is about seeming and not being. And people will settle for seeming and not being. Which is how you get a Donald Trump, to begin with. It's all seeming. And it's encouraging other people to learn to seem. Then you've forgotten what being is like."

Just then his mobile phone rings. It is a real ring, the kind you hear on a real telephone. He takes the call and informs me, apologetically, that he has to go. We leave the rehearsal studio and head downstairs. Standing outside in the rain under the canopy, he says goodbye and climbs into the waiting car.

As he drives off, I note that the entire time we were talking, while inadvertently holding a mirror up to himself, not once did he look in the mirrors around him. He was far too preoccupied with other reflections.