It’s not the tilting columns that make you smile, diverting though they are. Nor is it the mirrored walls that swerve and collide in random curves and playful angles. What amuses, as you walk through MIT’s Computer Science and Artificial Intelligence Laboratory, is the yellow hazard sign erected by students at an intersection of walkways. ‘Nerds x-ing’ it warns, under a stick man with glasses, rucksack and satchel.

It could be argued that I am here, in snowy Boston, at the Massachusetts Institute of Technology, to meet the king of the nerds, the godfather of the geeks, the ultimate web-lebrity (there is such a word, I saw it in The Guardian). But that would seem disrespectful. And Professor Sir Tim Berners-Lee, the man who invented the world wide web, deserves respect. He could have become a multi-billionaire by charging royalties for his invention. Instead, with Olympian selflessness, he gave it to the world for free. No charge. Help yourself. That was 15 years ago this April.

He is not just British by nationality, he is British by temperament. A reserved and modest man, he shuns the limelight, preferring instead to closet himself in academia – lecturing, working with research students, staring wistfully into space as he tries to solve a software conundrum. He rarely agrees to be interviewed and on the odd occasion when he does, you suspect it is merely out of politeness. He seems intense and nervy, his small, starey eyes flitting around the room like a cornered heron’s. But he has good bone structure, a toned physique and an air of youthfulness about him that belie his 52 years. Perhaps it is simply a matter of his reputation preceding him, but his greatness seems almost palpable, an aura that surrounds him like a Ready Brek glow. He was, indeed, voted the greatest living Briton in 2004. That was the year he was knighted. Three years after that he became one of only 24 people entitled to have the letters OM after his name. Not that he would use them.

His office reflects his unassuming, if slightly geeky nature (he considers the term ‘geek’ a compliment, by the way). There are sandals under his desk, an orange cagoule on the hanger, a rucksack on the table. His sheet-metal shelves are dotted with lever arch files, ringbound computer texts and even – how old fashioned – a book (Cybermetric Orientation Programming is its title). But apart from a small photograph of his wife, Nancy, the mother of their two teenage children, Alice and Ben, there are no pictures. The thing that dominates this room, inevitably, is a computer, one with a big, really big, flat screen. It’s a Mac, as far as I can tell, though he will not say because, as head of the World Wide Web Consortium, the impartial body that sets international standards for web use, he avoids endorsements.

That’s the thing about this place. As important to the computer world – and therefore the world generally – as Silicon Valley. I tell him I was surprised that I was able to walk in off the street without any security checks. ‘Well, we’re a campus. It wouldn’t be practical. We only have ideas here. There is more security next door. They have a nuclear reactor there.’

That may sound funny, but Sir Tim has no sense of humour as far as I can tell. When, for example, I ask him if he ever wakes up in a cold sweat in the middle of the night, screaming: ‘My God! I’ve created a monster!’ he blinks, cocks his head to one side and says: ‘No. Um. No, I don’t.’ He is a great blinker. And a fidget. Ironically for one who revolutionised the way the human race communicates, he is himself a fairly hopeless communicator. It’s not just that he ums and aahs, he also gabbles, clicks his tongue, gulps and, when excited, runswordstogether. And as he talks he makes notes. He is no good at remembering names and faces and, occasionally, he will spin round on his chair to Google the word he is looking for.

He first proposed the web in 1989, he tells me, while developing ways to control computers remotely at CERN, the European Organisation for Nuclear Research based in Geneva. The internet already existed as a series of computers linked by cables. His idea was to allow computers all over the world to talk to each other – through the internet, using a language of his devising (HyperText Markup Language, or HTML as it is better known). He never got the project formally approved, but quietly tinkered with it anyway, getting the first browser up and running on Christmas Day, 1990. The unwieldy name and initials ‘www’ – they have three times more syllables than the phrase they’re abbreviating – came about as a result of the inventor’s modesty. Originally he had come up with the name The Information Mine, but he found the initials, TIM, embarrassing.

On 30 April, 1993, Sir Tim’s browser was placed in the public domain. His invention spread across the planet like a cheer in a crowd, partly because it coincided with the growth in personal computers, partly because, thanks to the generosity of its creator, it was open to anyone. Now more than a billion people use the web and it has more pages than there are neurons in the brain, 100 billion by some estimates.

The concept of cyberspace, moreover, with its fathomless resource of information, has revolutionised the way we work, shop and play. Without Sir Tim there would be no Amazon, eBay, Yahoo, Google, Wikipedia, YouTube, Facebook, MySpace and, yes, telegraph.co.uk. It is no exaggeration to call his invention the most significant since the printing press. But it has also helped gamblers bankrupt themselves, fraudsters prey on the gullible, and pornographers sell their virtual wares; and, of course, it has created a sinister new breed of paedophile. That’s partly what I mean by characterising Sir Tim as a Dr Frankenstein. His monster could prove to be a force for good or bad. The jury is still out.

‘I had the idea for it. I defined how it would work. But it was actually created by people,’ he says. ‘So when you refer to the web as a monster well, yes, it has all these arms and legs but the arms and legs are humanity. The technology allows humanity to express itself and interact. If you are frightened of it then you are frightened of what humanity can do.’

And not without good reason… I ask whether he has heard about the copycat suicides in Wales, the ones in which 17 teenagers hanged themselves in order, it seems, to get on a virtual wall of remembrance on the web. He hasn’t and scribbles it down to look up later.

‘Well that has always been a fear,’ he says. ‘That the web will become cult-like because you can filter off your mail and form a cultural pothole with steep slippery sides where the only form of communication is people telling you to commit suicide. Another fear is that, because of the web, we will all end up speaking McDonald’s English across the globe and end up with a vocabulary of 2,000 words.

‘These are opposite fears: one that it will make everything too bland; the other that it will lead to cults and cultural potholes. But there are few global things on the web. There is no one newspaper read all over the globe because, actually, the web is composed of a tangled mess of groups of different sizes. They all interconnect, so you don’t have one mushy group. That is the middle path. Interconnected communities. That is how the world can survive.’

It soon becomes apparent that when Sir Tim refers to ‘the world’ he usually means the virtual world, the world wide web. ‘What the web does is change the shape of communication,’ he says. ‘For example, all these wormholes. It’s not on a sphere any more. The world is flat, as Tom… sorry, I’m not very good with names. The guy who wrote that… New York… I get name blanks. He wrote the, um, world is flat…’ Sir Tim spins round and Googles the name. ‘Friedman. Tom Friedman. He describes the world as flat but actually it is multiply-connected.’

In his Who’s Who entry, Sir Tim does not mention his family, but he met his first wife, Jane, while reading physics at Oxford and they married soon after he graduated (with a First). That was in 1976. They both went to work in Poole, he for Plessey Controls as a programmer, she for Plessey Telecommunications. He met his second wife, an American, in Geneva while working for CERN. That was in the late 1980s. It was through an amateur acting group. She was a software engineer and former figure skater. They married in 1990, the year he invented the web. On the ‘frequently asked questions’ section of his page, the question ‘Can you tell me more about your personal life?’ gets the answer: ‘No, I can’t – sorry.’

But ask him whether the web has brought out the best in people or the worst and he will purse his lips. ‘It has reflected humanity,’ he says after a brief stare out of the window. ‘I believe there are more good people than bad. I’m an optimist. Perhaps that makes me naive. But in general, people’s experience of the web has been positive – people who have saved a relative by finding out from the web what disease they had. But people complain about the smutty sites and the phishing, and the pretend bank sites trying to steal your identity. They also complain about the people who process information gleaned from the web without taking any trouble to find out whether it is true or not.’

I ask if he has looked at any porn sites. ‘Um, I haven’t spent a lot of time going into the goriest side of it, but I have logged on to a bunch of social networking sites to see how they work. I prefer more open protocols. I think part of the push for Web Science is that we realise no one understands the web in the way that we understand the brain. What would happen if we changed the parameters slightly? Email, for example, started as a friendly academic tool, it worked until people had the internet in their homes and restrictions on using the web were relaxed, and then it quickly reached a tipping point. Then the email disintegrated.’

Ah yes, all that spam about Viagra. ‘Exactly. It wasn’t designed for that. We now have to go back and redesign the technical stuff to cut down on spam. We also have to ask what happens to democracy in the internet age. Will the blogosphere end up being more exciting than, with all due respect, the Telegraph online? Who knows? But I think we will end up placing more importance on reliable reporting. Democracy depends on it. Otherwise people end up electing leaders purely on the basis of rumour and celebrity status rather than facts and science. Maybe with the web we can produce a democratic system that works even better. Applying all the brainpower in the world to solve problems.’

The comment reveals the high idealism that lies just below Sir Tim’s surface. Perhaps aware of this, and the immodesty that it might represent, he quickly deflates the conversation with a reminder that, actually, his invention was born of low practicality. ‘Partly I invented the web for myself because it was something I needed. A lot of ideas, such as the spreadsheet, were developed by geeks who needed them. I needed this. I wanted it for my job. My job was designing software for particle accelerators and physics experiments. I was working with a distributed group of people and I needed to reach them and gather their data. It was partly frustration. A lot of people express frustration at the software on their computers, but some have the ability to fix it. A geek will sit down – and I use “geek” as a term of high praise – and write a programme and fix it.’

Sir Tim believes that if his technology had been in his total control it would probably not have reached the critical mass it needed to reach in order to work. In other words, if he had charged royalties as well as asking every user to use the same Uniform Resource Locator (URL), large companies and geeks in garages alike would have dropped his invention. ‘There was a rival system to mine being worked on called the Gopher,’ he recalls. ‘That could well have been the one we are all using now if the University of Minnesota hadn’t tried to extract royalties for it.’

So, there we have it. Sir Tim insists it wasn’t altruism on his part, this business of not charging royalties, so much as practicality. But I’m not sure I believe him entirely. ‘No, really, it was just a matter of being practical. It was also to do with the ethos of the time. The spirit of the internet was not one of patents and royalties but of academic openness.’

He dismisses the notion, by the way, that his invention came to him in a eureka moment. ‘I think the eureka moment is a myth. I think our creativity is subconscious. It happens slowly… it’s not that you are really clever and you just thought it up, it’s because you’ve been washing dishes, skiing, talking to people, reading up, concentrating on different aspects of the problem. My hunch is that Archimedes spent a week thinking about the displacement of water, then eventually it came to him. I don’t believe it came to him in his bath. It’s a nice story.’

He also dismisses the suggestion that he has an exceptional mind. ‘I am an ordinary person. I was just a programmer with some useful experience that happened to line up with what I wanted to do with the web. I’m sort of bright and given to thinking about technical things, but then so are a lot of people. I didn’t have any magic. My boss allowed me to do it in my spare time and I put in the effort to write the code. It wasn’t because I was some kind of star.’

Even so, does he find that computer geeks are in awe of him? ‘Not people I work with, partly because I am so… well, my spelling is terrible, just terrible. We chat a lot on the internet and they always note how I can’t spell and how my letters arrive in different orders.’

This apparent dyslexia apart, he claims not to have many insecurities. ‘I think I’m middle of the road there, though throughout the web I was always concerned that it was going to break and there are still things I do worry about. There is also net neutrality, which I worry about. If large corporations control our access to the internet and determine which websites we can go to, we’ll lose its openness and its democratic nature. I think a lot of people are worried about privacy and inappropriate use of data.’

He tends not to dwell on what he might have done with the billions he could have earned if people had been prepared to hand over royalties. ‘It would be nice to be in Bill Gates’s position, where you could donate huge sums to tackling world health problems. We all ask ourselves what we would do if we had loads and loads of money. I would buy huge tracts of coastline in the UK and donate it to the National Trust. I’d also buy ugly buildings and knock them down.’

Diplomatically, he does not fuel the speculation that he is no fan of Bill Gates. ‘Um, I don’t know him… not, er, personally… do I? Er… let me think. One of the interesting things about inventing the web is that I do get to meet all kinds of people.’

I bet he does. He must be the Nelson Mandela of the computer world. Everyone must want to meet him. ‘Actually he’s an example. I did get to meet Mandela.’

As an adult, Sir Tim rejected his Anglican upbringing, which, he says, ‘relieved a great tension’. He certainly hasn’t replaced religion with materialism. Until recently he drove a 13-year-old VW Rabbit. ‘I’ve just replaced it with a little VW Eos. You’re right though. I’m not very materialistic. I enjoy being in nature, so protecting nature would be how I would want to spend money.’

Other than paying for skiing holidays, his pleasures in life come cheap. He likes ‘wandering around in shorts and sandals. Walking in woods. That sort of thing.’ He also plays the piano a little. And the guitar. ‘Ralph McTell songs mostly, although that was when I was a student really. I also listened to a lot of Steeleye Span then.’

His parents were both mathematicians and they worked on one of the earliest computers. I ask what it was like growing up in such a cerebral household. No television presumably?

‘There wasn’t an atmosphere of high seriousness, if that’s what you mean. The whole point about mathematics in our house was that it was fun. We were always joking. I wouldn’t say it was an intellectual house. For a lot of my childhood we didn’t have a television so it wasn’t a question of what to watch. What we did have was a drawer of scrap materials which I could use to make gadgets. A baring, or a nozzle, or tubing, or springs. I would glue things together. Washing-up-liquid bottles. I would make Airfix models as well, but they were too formal for me. I preferred my “scrapmat box” – scrap materials box. Then I got a train set and became fascinated in the electronics side of that.’

He was soon itching to build his own computer. At Oxford, after being banned from using the nuclear physics lab’s computer (thanks to an incident in which he hacked into it for rag week), he managed it. He built a computer with a soldering iron, an M6800 processor and an old television.

Happy, rebellious days. A far cry from the responsibilities he now has. As well as acting as a sort of regulatory authority for the development of the web, Sir Tim and his team at MIT are also working on the next stage in the web’s evolution, the semantic web. Its searches can be expressed in natural language, such as ‘Where can I find the nearest store with cheap Manolo Blahnik shoes?’

Having invented the web and changed the world for ever, did he suffer from difficult ‘second album’ syndrome? He blinks again. Does not smile. ‘The semantic web I’m working on is not a follow-up to the web, it is part of it. It’s about using one application in another. Putting my bank statements onto my calendar, say. It is about allowing your computer to understand what a date on a statement means. But that is not to say computers will be able to analyse what data mean in a philosophical sense, in the evening over a drink.’

Some evidence of humour, after all. Perhaps he has just grown used to Americans not getting British humour, and so has given up on it. Although he often comes back to Britain, Sir Tim feels part-American now. ‘It’s inevitable, really, being married to an American and having children grow up immersed in American culture. They have American accents. My American accent is probably less pronounced. British people usually think I have an American accent and the Americans usually think I have a British accent, so I guess that makes me in the middle.’

Berners-Lee is not an easy man to read, and is certainly not given to self-disclosure. Ask him if he’s sociable, for example, and he will tell you that on the Myers-Briggs test, he rates ‘pretty much in the middle on introversion v extroversion.’ In the middle again. As we have seen, he also believes there is a middle way for the web to develop, between suicide cults and McDonald’s blandness. Yet actually I think he is more exotic than this middling characterisation allows. And more romantic. All that walking in the woods. All those hippy ideals about sharing and democracy.

‘People get things wrong about me,’ he says as we embark on a quick tour of the building, starting with a black cube in the corner of his office which has the same NEXTSTEP operating system he designed the web on.

I ask what things people get wrong about him. He nods earnestly. ‘I only played tiddlywinks as a student to get a ride to Cambridge one day. I wasn’t a champion or anything. Things can get out of proportion.’