Strict adherence to health and safety conventions is not what evenings with David Blaine are made of. So the fire regulations of the Oxford Union have been daringly reinterpreted in order to cram some 600 eager sceptics and true believers inside the oak and leather debating chamber. The disembodied cries of the unfortunate many who are shut outside in the darkness tip in through the high windows: "Daaaviiid!" His name becomes a supplication. Within, a tall, smooth-shaven man in remarkably robust physical form is fielding catch-you-out questions from Britain's alleged educational elite with intelligence, wit and grace. Pretty good for a guy who, on the car journey from the capital to this crenellated seat of learning, was asking, puzzled, what Oxford was about.

It is 44 days to the night that Blaine completed Above the Below, the endurance stunt that saw him suspended inside a Plexiglass box by Tower Bridge in London for 44 days with only a water tube to sustain him. It was an undertaking unlikely to illicit lukewarm reaction. From the fractured friendships of late-night pub rucks to the saboteur who tried to cut through his water supply, swinging on the cables supporting the box and screaming, "Go back to America. We don't want you here," the response was extreme. Even those who considered him an irresponsible attention-seeker who should spare more than a thought for the unwilling starving who anticipate no end to their ordeal and have no movie deal in the bag were gripped. It was, whatever your stance, a national event.

Over dinner, before the speaker meeting commences, Blaine banters gamely with members of the Oxford Union committee, the kind of sweetly blustery boys who might exist now or 50 years in the past. He tastes neither the shredded bacon salad nor the fat slab of steak that are proffered, and sips from a glass of water. His partner, the model and jewellery designer Manon von Gerkan, holds up stoutly under cross-examination on her own thoughts about her boyfriend's antics.

Outside, the thrum from the waiting crowd gains momentum.

Inside the debating chamber, the questions are various. What about the hungry poor? How did you answer the call of nature? Do you reckon you could take Gandalf in a fight? He is an extraordinary and generous performer. The voice - cartoonish, devoid, too slow for comfort - suddenly galvanises in context. He makes deprivation sound great.

Granted, a certain amount of intellectual lassitude is required of the audience. "It wasn't a political statement," he says in answer to the Big Why. "I don't really know why I did it. It's like riding fast on a motorbike. It was just a dream that I had one day and I did it."

Even when he's kidding he still sounds a little touched. "Derren Brown [who performed the 'Russian roulette' trick live on television in October] is a great guy but I did say to him, 'Why don't you use a real gun and a real bullet and just fire it at your hand so that you have a one in six chance of getting your hand blown off but you don't die?'"

He is, however, superlatively kind to the bumptious baby orator who fluffs his question: "If you lost your life, would you regret it?" And this is perhaps where his senselessness most makes sense. He makes everyone else feel so certain that he is a fool that they forget to check their own foolishness. "If I lost my life," he responds cheerfully, "I'd be really angry."

It was not ever thus. The film of Above the Below, directed by Blaine's friend Harmony Korine, features a dirgeful riff on his hatred of life, his love of death and his passion for confronting people with the possibility of his imminent demise. It slips into an angry juxtaposition of his mother's uncomplaining death from cancer (when Blaine was 20) against modern consumer excess.

"That was how I felt in that moment, but it wasn't what I wanted to get across," Blaine tells me when we meet earlier in the day in a lofty hotel suite in central London. "I don't hate life, I love it." He worries that the lessons he learned inside the box will be impossible to keep hold of now that he is plunged back into the world of excess. "I think it's almost impossible. For example, when I visited Haiti - it's such a poor place, but what they have is love, what they have is friendship, the sunset, the trees; whereas in a country of excess we're focused on what car you have."

Surely this is nonsense, though. Most people in Haiti are hungry and miserable and frightened. "Yeah, I know that, but what I also noticed was that people there had a different way about them to people in London or America. They were so warm and appreciative."

Noble Savage delusions aside, what are the ethics of making a profit out of voluntary starvation and incarceration when so many face these circumstances without the succour of free choice? "You can say the same about people who run marathons when there are people in wheelchairs," he counters.

Later, driving to Oxford, he worries that this was a politician's answer. "What I really want to say is, don't you get it? This is what I want to do. As for those people with their megaphones spreading their negativity, go find a homeless person and give up one of your meals for them, then I'll pay attention.

"Hunger strikers have it much worse," he concedes, "because they have everyone against them. They have guards beating the shit out of them and putting food right in front of them. If I'd had food in front of me I couldn't have done it. I can't even control myself on an aeroplane. I need to eat, eat even though I don't want to eat that food.

"I don't get hungry unless there's food in front me, but if there is I can eat almost with no limit, which is terrible because it means I'm a binge eater, which is the worst thing you can do for your heart and your metabolism," he concludes fretfully. He sounds so concerned that for a moment one wonders whether the whole stunt was just the elaborate execution of an eating disorder.

Blaine also insists that his profit margins were negligible. "Money had nothing to do with it. I only made $100,000 on that. I know that that sounds a lot, but I can make that amount in one hour doing card tricks at a party for rich people. If it was about the money, I would have taken a Virgin mobile in there like they asked me to, and I'd have been selling things at the site and I'd have taken the Coca-Cola commercial that they offered me for $2m. We got Channel 4 and Sky involved because we needed the capital to hire the crane and set up the site. I'd much rather it was just with Channel 4, though. I had no idea Sky was going to do a live camera. I never watch TV and when I turned on Sky I realised it was nothing to do with what this stunt was about."

Blaine remains insistent that his intake was limited to water throughout the 44 days, and subsequent medical analysis would appear to back this up. "By day 35 I was feeling so clear-headed and focused, even though my body was in pain, that I wrote in my journal that even I'm sceptical [about the veracity of the stunt]. So I didn't feel angry with any of the sceptics because I was one of them. I didn't realise that the human body, any human body, is so adaptable and changes that quickly to become a survivor."

His blood is still being monitored by specialists who have leaped at the opportunity to study the long-term effects of starvation.

Blaine has a seven-year plan which he carries in his back pocket. It is written in blue ink on a frayed scrap of paper. He admits that it is a little out of date now. It includes "ice", which one assumes is a reference to his 62 hours inside a giant ice cube, and which came after seven days and nights buried in a glass coffin and before 35 hours on top of an 80ft column, then jumping into a pile of cardboard boxes below. His next one is to involve diving headfirst into a river from a great height.

He doesn't have a limit, he says. "Nor does anyone else. I don't differentiate between human beings." Is he an artist or a showman? "I don't see much difference. You're creating an image whether you're a showman or a painter. Art is perhaps a little more abstract."

He is ambitious, he says, but not for recognition. "As somebody who does performance, of course I plan things so people turn up and think about it. But my main objective is just to accomplish each one." He doesn't feel proud of his 44-day endurance, however. "I never really like anything I do. I'm always thinking of all the things I could have done differently."

Born in New York, and raised by his mother alone, Blaine says that he has always pushed his physical and mental limits, even if he didn't recognise that that was what he was doing. "I always thought that if I couldn't jump up and touch the rim of the basketball or swim six laps underwater, I would die a horrible death. When I was really young I would stop eating. I don't know why I did it. I think I just liked the feeling of being able to do something." He recounts all sorts of dangerous childhood deeds, but then children do like taking risks. Maybe he just never stopped.

Does he think that people read too much into his motivations? He sighs. "I think people always tend to do that." It was once said of Blaine that he was a sphinx without a riddle. More to the point is that we all project our own riddles on to him. When one ceases to psychologically eviscerate the man, the experience becomes a lot less elliptical.

He chats amiably about his hero, the writer Primo Levi. He calls up his favourite Guardian science correspondent and invites him to dinner. He tells me about Kate, a student at Oxford University who visited him while he was inside the box and held up quotes that he liked. He is going to meet her before the speaker meeting, and she was part of the reason that he accepted the invitation. He is intuitive about the people he meets, in an un-tricksy, thoroughly humane, way.

And here you have the truly magical thing about David Blaine. He doesn't do distance. Unlike most feted - and plenty of unfeted - individuals, he doesn't impress upon others their difference in status, whether in regard to success, or money, or gender. He is not a sleaze. He doesn't want to be adored but he does adore to be engaged with. And when he signs autographs he does so as though he is being paid a huge compliment. "I love people. I like creating an enigmatic persona but not keeping people at arm's length."

· The final Above the Below programme airs on Sunday, 21 December at 9pm on Sky One. The video/DVD from Channel 4 Video is out now