There is no doubt about it. Helen Mirren has a simmering sexual presence. Hot and cold, withdrawn and flirty, disciplined and out of control. When we meet in her hotel, she’s just finished eating eight croissants. She says it as if she’s rather impressed with herself. She says it without guilt, but kind of licking her lips.

Mirren is starring in the children’s adventure movie Inkheart. The film is about what happens when you have the ability to make characters from books come to life. In the film, she plays an eccentric aunt who rides a motorcycle very fast, Lady Godiva hair swirling in the breeze. She says she took the part for that bike ride.

She looked extremely comfortable on it. “Well, I didn’t have to learn because I already had a motorbike when I was in my early twenties. So I thought, I don’t care what else happens, I want to be on that motorbike again. I got it when I was in Stratford because I needed transport and I thought it would be cool, and also cheap, because I couldn’t afford a car. But it wasn’t cheap, because you have to buy all the clothes.”

You imagine Mirren in her leathers. Striking. “The major problem was, when you stop at a light: you can’t balance, so you have to put one foot down and hold the bike up.” She stands up and straddles as if riding a bike to demonstrate. She’s wearing a cotton suit in milky beige and a white T-shirt. As she bends down, the skirt stretches over her bottom and thigh. Extremely tight. “I wasn’t strong enough, so at every traffic light I would topple over. I had it for three or four months and thought, this is not working out. But on the movie set I could just go and stop, and someone would hold up the bike. It was lovely.”

Since winning her Oscar for The Queen, she has worked steadily and variably, thus avoiding the Halle Berry curse of Oscar, where everything you take on flops and your career backtracks. She was twice nominated for Tonys on Broadway — for Turgenev’s A Month in the Country in 1995, and for Strindberg’s Dance of Death, with Sir Ian McKellan, in 2002. She is about to start filming The Tempest. And she’s been working with her husband, the director Taylor Hackford (An Officer and a Gentleman, and Ray). Lots of zigzagging the planet. I’ve just come from LA; she wants me to have a croissant too. “Because when you’re jet-lagged you feel entitled to absolutely anything, don’t you?”

She asks a lot of questions of her own. Not as an aversion technique, which some interviewees employ rather than talk about themselves. She’s curious. Engaged, alert, curious. “My husband’s film is called Love Ranch. It’s a brothel in Nevada in the 1970s,” she says with a tiny but perceptible glint of naughtiness in her eye. Are you a madam? “Of course. I’m not one of the old girls,” she laughs. She could be — very many people would definitely want to have sex with her.

“Funnily enough, the older prostitutes are the most popular, because the guys think they’re user-friendly. They’re comfortable with them, so they don’t feel intimidated. And guys who go to brothels are not the most successful guys in the world sexually, so that’s what they need. It’s all about not being intimidated,” she says, managing to seem intimidating and inviting all at once.

I don’t think she was born this much of a sexual being. I think she earned it with wit, confidence, and intelligence. Her face is so animated. You see her feeling everything. Sure, there are lines, but it’s not the lines you notice. It’s not the age, which is 63. You just think she’s hot — not hot “for her age”. She says it was fun to work with her husband, and then qualifies her statement. “It was lovely to go home at night and be with my husband,” she corrects.

“Working with him, I have to say, wasn’t easy. My husband in work mode is not the easiest of people, although a lot of people adore working with him. But because I have the emotional connection with him, I would get upset if he was shouting — not at me, but at someone else, demanding something. I would be seeing it from their point of view. I would find myself rushing around trying to mop up after him.”

Then she backtracks again and contradicts herself, as she is prone to do. “But I love the fact that he got the film together and he created a wonderful role for me. But husbands and wives don’t need to work together. We are professional people in our own worlds. There’s nothing I love more than going to my husband’s set and being his wife. But this, it mixes the roles up. It either gets too cosy, which is not a good thing, because it’s not very creative. Or it gets the opposite…”

Which sounds like it was with you? “Yes. He didn’t make me cry, but he made me very cross.”

Perhaps the secret of their longevity is the fact that they hadn’t worked together since 1985, when they met on the set of White Knights. Mirren once told me it was because they came together late, as fully formed people. They eventually married in the Scottish Highlands in December 1997. “We came to each other grown-up, professionally formed. I was in my late thirties and I was just so aligned to him. We were generous to each other and loyal in terms of each other’s work.” Before that she had intoxicating love affairs with the photographer James Wedge, who liked to experiment with sexuality in his images, and the actors Nicol Williamson and Liam Neeson. The latter says he adored her because she taught him sophistication and how to eat prawns. There’s only a hint that she wasn’t always as well put together as she seems today.

She says she cries easily when it’s with pleasure. She cried at Inkheart’s happy ending.

“I always cry at peculiar times. For example, I weep openly if I see a parade, or people marching down the middle of the road, especially if they’re dressed up in their best. I think it’s because they’re trying so hard. Spelling Bees make me cry. Marching bands with drums, I’m in bits. The Olympics made me cry.” She puzzles: “Isn’t that strange?”

What is also strange is, after the year she collected her Emmy for playing Detective Superintendent Jane Tennison in stripper shoes and a Marilyn dress, and her Golden Globe and Oscar for her emotionally hemmed-in performance in The Queen, she should want to follow it with a children’s film and play an aunt who doesn’t really like children. Is that like her? Does she like children? “I’ve never been hugely maternal, but I’ve always loved children as an aunt, a naughty aunt. I’m very happy to be able to give children back to their parents… Not that I’ve actually ever been alone with them.” She’s never wanted to have children of her own. She decided that when she was about 13 when she saw a film at her convent school of a woman giving birth.

“Out of our whole class there must have been more than me who were traumatised by it to this day. It was horrific and it gave me an absolute horror of childbirth. I suppose my local council must have had word down from the government that we had to have sex education. We had no mention of sex in my school, even in biology.

So they herded us all together into a room with other girls the same age, and boys, and this dykey woman in short grey hair said, ‘What you are about to see is a miracle.’ And this film starts and it’s a midwives’ instructional film. There was no sound, just the camera going whirrrr, and words would come up at the bottom: Now prepare the rubber sheet. The lights came up at the end and every kid was white and sick and silent. The boys couldn’t look at the girls and the girls couldn’t look at the boys.”

So there it was, a pivotal moment in the young Helen’s life. She was destined never to be a mother and never to mind about it. I wonder if this adds to her particular kind of sexual omnivorousness. My boxing trainer, who had been in the army, used to have her picture as a pin-up. He said: “Everybody in the army fancied her. We all had posters up, because the thing about her, even though she was older, she was never going to be your mum.”

Most men are prone to a Mrs Robinson fantasy syndrome. They like older women because probably their first sexual awakening was from one — a teacher or a friend’s mother. Someone excitingly unreachable was just more loaded an attraction than the 12-year-old girl they sat next to in geography. I think men get excited by her experience. They hope to learn something and take it away. The take-it-away part is also very important to the appeal of the older woman. The older woman is not for ever; she’s transitory.

It’s in the moment. No strings, no biological imperative. It’s not long-term. There’s no pressure. Men don’t have to take a lead — they can follow. And also, she might be grateful.

Mirren laughs at the thought of the boxing trainer’s devotion and says: “Oh, fabulous. And he’s absolutely right. I was never going to be anyone’s mum or grandmother. But I can dig that beautiful earth-mother thing, feeding the masses. I’m thinking of Nigella Lawson. Does she have children?” She does. “Do you know what I mean? She’s sort of gorgeously fertile. That’s sexy.”

Mirren is quick to assert her sexuality isn’t in doubt: “I actually won my first Golden Globe for something called Losing Chase. Kyra Sedgwick and me fell in love with each other, and it was a lovely piece about women loving women. In my heart of hearts I love women more than I love men. I mean sexuality aside — I’m heterosexual.” She pauses to rewind.

“I guess I’m heterosexual. I loved my friend I had at college because there was a sense of camaraderie and physical closeness that doesn’t have to be sexual.” I wonder.

Mirren is quite a tease. In her last interview she talked about how much she liked to take cocaine at parties. She only stopped using the drug when she realised that Klaus Barbie was living off the proceeds of others who made their money from cocaine in South America. Then she told another magazine that she’d been raped and never bothered to report it. Now she’s saying that she loves women “in general more than men”. But she has requested in the past that she be interviewed by a man because she gets on better with men. Was that true, then?

“No, it’s more that I prefer male journalists because there’s a streak of female journalism — the bitches — who are mean-spirited and nasty because you are another woman and want to make you feel crap. It’s very upsetting. I’m more careful when I’m being interviewed by a woman because, from experience as well as reading articles about other women, I know there is a little stiletto knife hidden behind the back.”

She’s laughing as she sizes me up. But she’s right. On the whole, women don’t like other women, because women are competitive with each other. She says: “In a rape case the courts in defence of a man would select as many women as they could for the jury, because women go against women. Whether in a deep-seated animalistic way, going back billions of years, or from a sense of tribal jealousy or just antagonism, I don’t know. But other women on a rape case would say she was asking for it. The only reason I can think of is that they’re sexually jealous.”

We’ve gone from talk of loving women to hating women in just a few seconds. We talk about jurors in rape cases saying the victim “asked for it”. “Yes. That is terribly unfair. And that used to happen, didn’t it, in those days.” She says this with concern, perhaps even empathy.

She has said in the past that when she was forced to have sex against her will it was the lethal result of a combination of feminism — not wanting to be a victim — and innocence — not knowing how not to be a victim. She has said that it wasn’t about just saying no, because the man wouldn’t take no for an answer. When you see Mirren as vulnerable, it skews your judgment of her and you understand all those layers of confidence that have appeared over the years and how they could be torn away very quickly.

Did she learn to be more confrontational? “No, I am not confrontational at all. I met a great guy, then another great guy, and had a series of fantastic relationships with nice men.” And that healed her. “Until that point I was thinking men were horrible; they were boring, boorish, vulgar, selfish and arrogant. Then I met a guy who was funny and lovely to me and I loved him. That was Ken, my first boyfriend. I learnt from wonderful men, wonderful relationships. They gave me support, made me feel good and made me laugh. Now I think men are absolutely great.”

She’s quick to agree that her early antipathy towards men is because she went to an all-girls school. “Absolutely. I don’t blame it. But I was 18, suddenly in London, and I’d never been out past 11 at night before. I never thought, ‘I will never have sex till I get married,’ because I never wanted to get married. So sex was on the cards, but I wanted it to be incredibly romantic. I decided it had to be snowing.” And was it? “No, of course not. It was probably a disgusting rainy night, but I can’t remember.” Was it with some random boy? “Yes.” Did you ever see him again? “I don’t want to talk about that. Sorry.”

Suddenly the air is thick with imaginary needles of pain. What did she learn from that experience? “I didn’t learn anything. I learn from the positive, not from the negative, but I do believe in getting on with it. Taking responsibility for yourself and not blaming other people is an incredibly important thing.”

This is key to Mirren’s mystical sexuality. She can be vulnerable, but she’s never going to be the victim. It is attractive. “But I’m not particularly competent, actually, in terms of answering phone calls, getting things done. I put on a good game. So to people like you I look incredibly self-confident and on top of everything.”

You mean you are acting? “Yes, kind of.” You are acting in this interview? “Kind of. Sometimes I blow it. I’m certainly incredibly vulnerable as far as my career is concerned. I’m full of self-doubt.”

But you’ve got an Oscar now. Surely that says: don’t doubt it. “It doesn’t stop you getting up and having to do it again.”

Suddenly I notice her tattoo, a little naive star on her hand. She did it on impulse in an Indian reservation in Minnesota, many years ago.

“I just wanted the tattoo and I was a bit of a bohemian. I got it when women did not have tattoos. Now girls are covered in them, like Amy Winehouse.” The tattoo is not particularly pretty, but it’s a symbol of her going against the grain and a kind of fearlessness despite the self-doubt. A psychic once told her she wouldn’t have success till her fifties, which devastated her at the time.

She was born in London and brought up in Southend-on-Sea. She was the daughter of a taxi driver whose father had come as an emissary from Russia to buy arms during the Russo-Japanese War in 1917. He was unable to return home because the Bolshevik revolution had started. The Bolsheviks confiscated the family’s estate and he was to be separated for ever from his seven sisters. Her Russian name, which she was born with, is Ilyena Vasilievna Mironov. She made an emotional pilgrimage last year to the family’s old estate in Russia and family in Gzhatsk near the city of Smolensk, 250 miles west of Moscow, and she’s always had a passion for Russian roles: she’s set to play the wife of Leo Tolstoy in the upcoming film The Last Station.

At the start of her career she felt marginalised by being blonde and big-breasted. She felt dismissed. Perhaps that’s why she could play the frumpy Queen and the tired Tennison so comfortably. She was confident of her own sexiness and didn’t need roles to prop her sexuality, although she played plenty of sirens too. She’s been Cleopatra and Lady Macbeth, and naked a slew of times, notably in The Cook, the Thief, His Wife and Her Lover, and Calendar Girls. “As you get older, naked stuff gets easier. It’s more to do with the role than what men in the audience think. There’s a liberation about it.”

You imagine her to be so confident about her body that she must be extremely attentive, with workouts and healthy regimes. “No, I’m very lazy. I go through phases of exercising. You know, if you start getting puffy when you go upstairs, I will force myself back into minimalistic exercise. I’m a great believer in the Canadian Air Force exercises because they only take 15 minutes.”

They must be working for her — the famous shots of her looking fit and slim in a red bikini flashed across newspaper pages round the world — but she dismisses them immediately. “I feel very lucky. I thought, ‘I wish I looked like I do in those pictures,’ because I don’t look like that at all. They’d just been taken at a great angle. The next day I started exercising because I thought, if I exercise, maybe I’ll look like that.”

Have you ever felt the pressure to look a certain way for a part? “No, but I’ve done it to myself. I mean, actors are always on a diet. It’s lovely to get a great role. Then you think, ‘Oh, I’ve got to go on a diet.’ My whole life I’ve gone backwards and forwards the same 10lb. I can wear clothes from 20 years ago. At my thinnest I’m a couple of pounds under nine stone; at my fattest I’m a few pounds under 10 stone. I’ve gone through many diets that are also very boring. You stop eating, and that’s what makes you lose weight: not eating. But as you get older, losing weight doesn’t make your body look better, don’t you think?”

We change the subject to Russell Brand, the latest younger boy to talk about how much he fancies her. “I don’t know if I fancy him. I haven’t met him yet. I’ll decide when I do. Talent is sexy. I love that alertness. I think Frank Skinner has it, and Jonathan Ross has it, and they are a little bit radical. I love those guys, and Russell Brand is definitely one of them.” So she concedes she might fancy him — this was before the radio prank-call scandal.

All the men in her life have had one link. “They have all loved boxing. So through various men I have watched a lot of boxing. I do love the human drama of it.” When she’s not talking about working with Hackford, she talks softly about him. She talks about building things, like their flat in New York and “the ruin we are renovating in Italy”. “It’s going to take up all of our spare time until we are too old and too poor to live in it… But it’s incredible fun.”

In Inkheart some of the characters who have escaped from books have the book written all over them. If she had to have a book written all over her, what would it be? “I would have verses from The Song of Solomon, which is so beautiful. I would want beautiful things written on me that people could read and go ‘wow’.”

She beams mesmerisingly.

As I get up to go, she stops me and says, “And thank you for the view.” I blush. I was jet-lagged, I had no clean underwear, so I’d gone without. I didn’t think she’d notice. But she did. And she laughs, the minx.

Helen Mirren’s latest film, Inkheart, is released in the UK on December 12

So how many friends do you have, Mark?

It's the world's biggest social-networking site, turning its 24-year-old founder into a multibillionaire in just four years. Simon Garfield meets Facebook's Mark Zuckerberg

24-year-old Mark Zuckerberg pictured at London's Excel Centre. Photograph: Phil Fisk

I was told not to expect a human whirlwind, but when Mark Zuckerberg walks into the room there is barely a breeze. He is 24, on the short side, shy in the way that short, ginger-haired people often are, and he walks with his head down, as if he is carrying a heavy burden, such as being the richest young person in the world.

Zuckerberg, the founder of Facebook, has one thing that most geeky-looking guys don't have - $3bn. Unfortunately, he doesn't actually have it with him, it is paper money, an estimate of his net worth. But the money is mentioned every time he is written about in the newspapers, as if it is an extension of his name. The sum was calculated when Microsoft paid $240m for a 1.6 per cent stake in Facebook in October 2007, valuing the company at $15bn, of which Zuckerberg owned 20 per cent. In these recessionary times Facebook is probably worth considerably less, but who knows? A company like his has never faced recession before, and hundreds of new customers are still flocking to it every hour. It is a genuine internet sensation, and it shows no sign of becoming less of one because it is based on an idea so simple, and so fundamental to our emotional and personal growth, that when people discover it, even four years after its formation, they feel that it is exactly what they've been looking for all their lives. They feel it is designed exclusively for them, and that is its trick: it makes more than 100m people feel like treasured individuals.

Facebook is based on the idea of sharing. Not long after he walks into the room (an almost empty conference room apart from a table with tea and biscuits and a photographer readying his gear), Zuckerberg tells me 'sharing' was the only word on his mind when he dreamt up Facebook in his college dormitory at Harvard in 2004. He was not thinking about money, nor personal aggrandisement; he just wanted to know more about the other students in his year. Harvard produced the traditional yearbook with grinning pictures and brief biographical sketches, but it would take a long time to appear each year and would be impossible to update until a year later. It also wouldn't contain one vital piece of information: was that person you found attractive in your class single or 'in a relationship'? Zuckerberg thought he could do something better online. You could put up as much personal information as you liked - your favourite bands, your favourite hobby, even your real name - and you could change it as situations changed. Four years on, his vision is in every street in almost every country in the world.

Zuckerberg has expanded Facebook to the point where it is among the fastest-growing websites in the history of the internet, but he says the principal mission is the same: sharing. In fact, he uses the word so many times that I wonder if I am talking to a machine. 'The idea was always, tell people, "share more information",' he tells me. 'And that way we could gain more understanding about what's going on with the people around you.' He says there are 12.5m registered users in the UK who share. Aaron Sorkin, the creator of The West Wing, has announced that he will soon be sharing the story of the birth of Facebook in a movie.

'People have always spent a lot of time communicating, connecting, sharing with the people who are around them and are important to them,' Zuckerberg continues. 'It's a very human thing. Facebook helps you share more efficiently with the people you talk to all the time, your family and close friends, but I think where it really excels is helping you stay connected with the people you know but don't get to talk to that much.'

What started this quest for knowledge?

'All my friends at school, we always talked about how the world would be better if there was more information available, and if you could understand what was going on with other people more - essentially if people shared more information about themselves.' A forthcoming book about Facebook has another theory: it was Zuckerberg's way of meeting women.

Zuckerberg looks up at the ceiling. 'Is it me, or is there a killer echo in this room?' he asks in his deep voice. There is a slight echo, and it is enough to prompt one of his advisers (he is accompanied by two, a man and a woman) to ask if he would be happier moving to another room. But Zuckerberg decides to stay put. He is at ExCeL, an exhibition and conference venue in London's Docklands, at the tail-end of a European visit that has taken in Germany and France. He has come to take part in something called the Future of Web Applications, those little pieces of software that let us simplify and glorify our lives online. His contribution will take the form of a 'fireside chat', but he won't be wearing dressing gown and slippers, he will be wearing what he is wearing now, which is what he always wears - jeans, T-shirt and dark North Face fleece. Zuckerberg, like Steve Jobs in jeans and black polo neck, has a uniform, and it is exactly what he wore on the day he began to get rich. There is a photo of him taken more than a year ago at Facebook HQ in Palo Alto, California, and he is wearing the same clothes. In a photo taken to accompany a magazine article at the end of last year, the fleece is identical. Sometimes he takes the fleece off, such as when he poses for our main picture. But when these shots are done, he feels a little naked and starts to pull it on again. 'Are you cold?' the photographer asks him. 'Not really.' 'Well, it would be great if you kept the fleece off.' Zuckerberg looks over at his advisers, shrugs, and then puts it on over his head. By way of explanation, one adviser says her boss is 'a pretty fleece kind of guy'.

It doesn't cost anything to join Facebook, apart from the best part of your waking life. Once you register, and perhaps post a photo of yourself, you may feel you are connected to the whole world. Perhaps you begin by searching for all the people in your email address book (this takes one click), or all the people in your company. Once you locate someone you know you can ask to become their friend, and you can see all their photos and all their friends, and soon you could be arranging events, or creating groups for like-minded people (wood-turners in Yorkshire), or writing on your 'wall', or sending someone a virtual hug, or just telling people what you're up to. 'Simon is eating cake,' might be one such message, and suddenly your distant cousin in Ontario will say that she, too, is eating cake, and in this way nonsense can be shared; your site is a multi-media text message to everyone you know, all at once. Then you log on the day after, and you find that manufacturers of cake stands want to sell you something. This is the most effective and newest form of advertising, not only direct but subtle, as if your computer understands your basic needs. It is how Facebook makes its money.

A couple of years ago, Facebook was just another of those social networking sites we liked to call Me Media or Media 2.0 - MySpace, Bebo, Flickr, Friendster, Orkut - places where you could go and be yourself (or pretend to be yourself) and put up music and photos. Facebook was already an online epidemic, but it was confined to universities. These days it is available to anyone over the age of 13, but this alone isn't sufficient to explain its phenomenal popularity. Other sites have come up alongside it - most notably LinkedIn, the biggest network for the workplace - but none has rivalled Facebook's rapidly expanding activity areas or its invasiveness. Millions access and contribute to their Facebook page on their mobile phones, and millions more have Facebook as their computer homepage with so many inbuilt applications linked to it free of charge. It has become the hub of a communicative digital life, a place where more than 100m photos are apparently uploaded in the UK every month, a platform for news and games, and a world of shopping that has extended far beyond the site's original concept as a slightly voyeuristic dating site. When the company changed the layout on everyone's profile pages a few weeks ago, the outcry was bitter and prolonged. It was as if Zuckerberg had personally come round to shift the seating arrangements in your living room.

Despite his love of worldwide sharing, the founder of Facebook is less keen to share information on himself. His Facebook page lets you know that he's a little tired after his European tour, but it's fairly tame stuff compared to the 'I had the best sex of my life last night' material volunteered by others. I have been warned against asking about how his life has changed by being a paper billionaire, so I ask him how his life has changed since Facebook took off. He doesn't answer immediately, but looks to his two advisers. One of them suggests that the better question would be how he spends his day. Zuckerberg is happier with this, and his response is masterfully boring: 'A lot of it is focused on product development. There are a lot of meetings and talking to people now, rather than doing code like I did a few years ago.'

I wonder if he has any mentors.

'A lot of the times the way I answer that question is, there is this guy who runs the Washington Post called Don Graham who I've looked to for a while because he takes a very a long-term view of things. And what we're trying to do - Facebook is really not a short-term thing - it's a 10, 15, 20-year thing.'

There are one or two other things we can glean from established sources. Zuckerberg was born in an affluent suburb near New York, where his father was a dentist. He was precocious with computers, and was offered jobs at Microsoft and AOL while still at school. For later information we can go back to his old college. The Harvard online alumni site, 02138mag.com, recently took against Zuckerberg, spurred perhaps by jealousy, or the fact that he didn't complete his course and still ended up richer than all of his classmates combined. The article obtained his original application to Harvard, in which he stated he was very interested in fencing. He found it 'the perfect medium... I rarely find myself doing anything more enjoyable than fencing a good bout.' The story also found that he was skilled at Latin and Greek, and had once built a computer version of Risk, a game of world domination. It declared that he has 'a dry, mischievous sense of humour that sometimes verges on obnoxious', and that he had a preference for Asian women. The article began with Zuckerberg at a developers' conference in San Francisco in 2007, and he was wearing a T-shirt and a North Face fleece.

Much of the information on Zuckerberg was based on court records filed when he became legally embroiled with the founders of a social networking site called ConnectU, which also began at Harvard. In fact, ConnectU began at Harvard at about the same time as Facebook, and Zuckerberg was involved in the early computer coding for the site. ConnectU argues that Zuckerberg stole their ideas; Zuckerberg counterclaimed that ConnectU later stole a large chunk of Facebook users' email addresses. The first legal papers were filed in 2004, a few months after Facebook took off, and concluded in an undisclosed settlement earlier this year.

Before meeting Zuckerberg at ExCeL, I go to see Blake Chandlee, sales director at the Facebook headquarters in London's Soho Square. It is an open-plan office in which a group of young people ensure that everything is running well with the site and then try to sell advertising on it. It has imported some legendary Silicon Valley karma, such as a very casual dress code and chalkboards on which staff are encouraged to write inspirational messages. On my visit, one of these reads, 'Gavin - he's massive!'

Chandlee is 41, a fun and open man, a perfect exemplar of the Facebook ethos. He tells me he is into honesty and sharing, but I am also informed that the Facebook high-ups in California would rather I didn't quote him directly. He told me Facebook was not such an amazing technological feat - it was just a group of tools and platforms. He called it an evolution of communication, as if that was a small thing. He also shared a little information about Zuckerberg, saying that he is highly focused on growing the business and that although he was a shy man and not a big personality, he was a deep philosophical thinker. He reminded him of a young Bill Gates.

Chandlee shows me many charts and graphs on his computer, including one that showed the fastest-growing user age was over 25, and one displaying the correlation between its users having a party one day and the hangover the next. Chandlee also demonstrates the rudiments of the advertising set-up, how anyone from private individuals to multinational companies can spend money to reach Facebook users by paying, say, 50p for each person they target. It is an impressive display, and it emphasises how much information Facebook can draw upon from its 100m-plus users. It knows, for example, how many people say they ate a Kellogg's breakfast cereal that morning. It can tell how many declared they were having a very bad day, and how many shortish people with ginger hair are indeed shy. As they used to say in 1945, let's hope they use it for peaceful purposes.

A few days after meeting Chandlee, I ask Zuckerberg about Facebook's responsibilities. No one so young has ever held the key to so much personal information; the sheer scale makes the data lost recently on MoD and NHS discs look like dropped homework. He replies that the most important thing in Facebook's success is the trust its users place in its security software (Facebook has received bad press following reports of cyberstalking). In the last few months the site has greatly increased security controls to ensure that personal information is seen only by those the user has pre-approved.

But Facebook is happy to share our information anonymously, specifically with advertisers, and potentially with political organisations; the site represents the biggest and most immediately responsive focus group in the world. 'What we try to do is have a neutral platform,' Zuckerberg says. 'Facebook doesn't have an opinion about specific things, other than "people sharing and communication around topics is good". So everyone has a voice, and people can organise around whatever they want.'

There is now an online feature called Facebook for Good, in which people write about how they have used the site to help themselves or others. Zuckerberg mentions how, when a hurricane hit, people used it to send messages to people around them to say they were OK. 'Here in the UK, there's quite a large group trying to organise raising awareness about knife crimes, and, on a lighter note, there are an enormous amount of people who organised because they really wanted Cadbury to bring back the Wispa bar.'

But what about Facebook for bad, those looking to increase support for terrorism or race-hate groups? 'The way it works is that if anyone on the site finds something like that and they want to tell us about it, then they can write in. There is a balance there. On the one hand we want to be very neutral, but at the same time we are really careful in not allowing hate speech.'

So the community regulates itself?

'It's a set of different communities. The idea isn't that Facebook is one new community, but it's mapping out all the different communities that exist in the world already.' Some of these Facebook does not like - the breastfeeding community, for example, who offended the company's sensibilities when mothers posted pictures of themselves feeding their babies with too much undone blouse.

And then there is Facebook for really bad. It is inevitable that when an institution reaches a certain size, it will attract crazy headlines, and a few weeks ago we had the 'Facebook Murder', in which a man was found guilty of murdering his wife in south London after she had thrown him out of their house and changed her Facebook status to 'single'.

I ask Zuckerberg if there is anything in his background that he regards as a key point in the development of Facebook - was he a lonely child with no friends, for example?

'When I was growing up, I was really interested in computers and making things, and when I went to college I studied computer science and psychology, which is pretty interesting for what we ended up doing, because Facebook is really at the intersection of these two things.'

That's a fair answer on a hobby level, but I'm thinking more of family. Did you ever wish you could communicate more, and more easily, when you were a kid?

'I don't know. I haven't thought that much about that.'

Instead, Zuckerberg spends much of his time thinking about how to keep Facebook expanding exponentially, and to keep people logging on (it is common for users to have a Facebook crush for a couple of weeks, a period where they say 'this is amazing', and even contact people they have never much liked, but the interest swiftly cools when they realise how much time it can consume, and how empty that level of communication can turn out to be). 'We're not focused on being cool,' Zuckerberg says. 'We're focused on sustainability, and what we're really focused on is not how much time people are spending with us, but how much they're sharing.' In a year's time he says he sees Facebook having millions more users. And in three years? 'Hard to say, but a lot of the same stuff.'

Zuckerberg then retires for his nap and readies himself for his public event later in the afternoon. As he rests, Facebook has sent a warm-up guy into the main hall at ExCeL, and he is demonstrating something called Facebook Connect, which he says is designed to make the web 'a more social place'. Dave Morin talks very fast and says things like, 'You guys really want some how-to stuff.' There are three aspects of Facebook Connect, and one of them is called Feed. 'As you look out across the web,' Morin tells his attentive audience, 'your friends are doing many, many different things. You do things like Tumbling, Yelping about your favourite restaurants, Twittering about things that you care about and what you're doing every day, you also Digg things, articles that you think are interesting, you blog, and all of your friends are doing this too.' (Translation: Tumblr is another multi-media sharing site, Twitter is a microblog, where you leave little notes saying what you're up to, Yelp.com is a place to recommended places to eat, shop and party, Digg is a news and info sharing site.) 'But the real question is, if one of your friends does something on the web and you don't know about it, did it actually happen?' A Zen question, with a Facebook answer: because of Facebook Connect, you will now be able to know exactly when one of your friends updates and changes any of the applications on their site.

'And now I'm gonna do a couple of demos,' Morin announces. This is a very risky thing in the technology world, a live demonstration of a new product. If something can go wrong, it will, and so it proves. Morin decides to connect to a demo of a site called Runaround, in which you can publish news of your jogging activity. 'Let's see if I can get it to work here... so basically it's a site where you can talk about the runs that you've done, share that kind of information with your friends... ooops, it's a little bit big... sorry about the demo, the Gods of demos aren't liking me today... when I press Connect with Facebook it pops open a window...' Only it doesn't. 'Maybe I'll have to switch to a different network here... sorry about this...'

Then it is Zuckerberg's turn on the platform, and the little boy in the fleece steps up to great applause. He is asked what most excites him about Facebook Connect, and about how the developers in the audience can use it to best effect, and about how his life has changed in the past four years. In every answer there is one common message: everything is designed to help us share more. Many in the audience nod in appreciation, for what could possibly be wrong with that? The more we share, the more we will learn; the more we learn, the more we will know; and the more we know, the happier we will be. Facebook will also be happier, and progressively wealthier, and its advertisers will be both as well, so that in the end it may be impossible to tell sharing from spending, and community from commerce.