Because of their human scale, the half-dozen sculptures waiting to be shipped out of Antony Gormley’s cavernous studio in north London seem as mortal as the half-dozen technicians welding, grinding and winching around them.

Some of the sculptures are bubble wrapped, others crouch on the floor or defy gravity by leaning out from the wall, others still are standing in the middle of the room, passive observers of the industrial scene around them: the flying sparks; the echoey screech of metal cutting through metal; the rattle of chains.

Part of the appeal of Gormley’s sculpture, from the vast Angel of the North on a hill in Gateshead to the army of tiny clay figures with which he won the Turner Prize in 1994, is the way we, the viewers, project on to them. And here, as I sit in his studio watching our photographer finish her portrait of him, I do find myself thinking of them as alive.

It would be as well to begin by describing what Gormley looks like, given that since his first major work, Bed, made in 1981 – a double mattress made from slices of bread, out of which he had eaten his own body shape and weight – his work has nearly always involved casts of his own body. So: Gormley is a tall, trim man in a white T-shirt and white jeans. His hair is cropped short and he wears rimless glasses. He looks about 42, but is actually 20 years older than that.

His manner is that of a slightly distracted academic, which is sort of what he is (an honorary fellow of Trinity, his old college at Cambridge). Though he is articulate when discussing his work, his speech is ponderous. He stands close to you when he talks, an invader of personal space.

He shows me one of the models that have been cast from his body, a figure sitting with its legs tightly drawn in. “I had to be strapped in for an hour for that,” he says. Shrugging off my inevitable question about pins and needles, he adds: “It was worth it.” The comment seems all the more remarkable when you consider he suffers from claustrophobia, a condition he has willed himself to overcome.

Though he claims he is fine today, he ought to be jet-lagged, having just flown in from Tokyo. Before that he was in Hong Kong, New York, Washington and Brasilia, 20 days of installations, exhibits and talks. But I imagine he’s quite like this all the time. A little lost in his thoughts.

He shows me a model of his latest work, called Model, which went on display at White Cube Bermondsey this week, but which isn’t finished on the day I meet him. To say this project is ambitious doesn’t begin to cover it.

It is a reclining body composed of cubes and is so big – 100 tons of sheet steel, 105ft long and 18ft high – people can walk through it. You enter through the foot and journey through its interconnected internal chambers. It is, in other words, both a sculpture and a building. “You and I might be able to see that that is a lying body, described in the language of architecture,” he says. “But I think coming into the space, you’re never really going to be able to tell what the hell it is. It’s going to be a dark, labyrinthine, cave-like experience.” It’s not obvious that it is a human figure, then. “An early idea was that we would not allow people to see the outside at all, but then we decided there should be a room in which you can see dozens of scale models of it. So the idea is that, in a sense, we are modelling the body, but we’re also mining it.” He’s not sure yet whether viewers will need to go through it one at a time, but will there be warnings for claustrophobia sufferers? “I think there probably should be warnings. And for people with heart conditions, because the thing is, it will be quite acoustically alive. I will have to dip slightly to get in.” (In the end, visitors are asked to sign a warning notice before entering.)

So, a big question for a big work of art, what does it, um, mean? “I suppose, the concept of the show is really just to say, ‘How can we rethink the model?’ Because it has so many contradictory meanings, doesn’t it? It’s either the perfect model, the aspired to perfection, or it’s just something that you have to copy, the scale model of something. Or is it a real body that you’re using as your reference?” And did this start, as usual, with his own body? “Yeah, yeah, but this was actually not started the way that most of the work starts, in other words, with a cast.”

He says he doesn’t know how people are going to interact with Model until they start using it, and that is a consistent feature of his work. He didn’t mind the appearance of bikinis and hard hats on his life-size figures on Crosby beach, and he loved it when Newcastle United fans fitted out the Angel of the North with an Alan Shearer shirt. “People had interpreted it in their own way, and taken ownership of it. That was a baptism, in the manner of the tribes of the North – they were unified in their love of football but pretty uncertain about a namby-pamby thing like art. So it was a really important moment.” What was the initial reaction to it? Did the good folk of Gateshead, er, reserve judgment? “When they heard that there was going to be a 200-ton, 65ft-high rusting angel on their hill, they weren’t very thrilled about it. But once it was there, they got very enthusiastic, from the moment it arrived, actually.” Does he enjoy watching people’s reactions as they first encounter his “public art”? “Yeah, and I’ve now asked for catalogues not to simply show the isolated object in beautiful whiteness, but instead show how people interact with the work.” He shows me a picture of one, Horizon Field Hamburg, a large platform suspended 24ft above the ground. “So this is just a plane, 50m by 25m, but it invites action. In the end, this became a catalogue of how people chose to interact with the strange, uncanny feeling of being in the air. This was an instrument for people to propriocept.” Blimey. Propriocept. No, I didn’t know either. It means observe themselves perceiving their own bodies. It’s obvious from these photographs that the spectators are having fun rather than being earnest and contemplative, which is how people often think they have to behave in galleries. There’s something about the formality of the gallery, I say, that prompts a certain awkwardness in people, they go into character slightly – become the “gallery goer”.

“Yes, I suppose as a viewer you are on show, in the same way that the works are, because everybody can look at you. But with this work,” he holds up the picture again, “eve rybody learnt from everybody else. I did get everybody to take their shoes and socks off, prior to being allowed into the space at all, so there was a sense in which there was a loosening of the normal rules of gallery behaviour, but it was the kids that really loosened everybody up.” I suppose before art became elevated as an intellectual endeavour it wasn’t on a pedestal at all, just part of our everyday life. “Yes, I like playing with that idea. I think it’s probably the Dutch who are to blame for starting the whole ‘art business’, because before they came along art was attached to relatively stable structures, and it was everybody’s. It was like going to the movies.” Making art accessible to everyone, and engaging members of the public in the making of it, has been a recurring theme of his work, most obviously realised in One & Other (2009), a project in which 2,400 people took it in turns to spend an hour on top of the Fourth Plinth in Trafalgar Square.

But that plinth idea divided the critics, as they say, and it drew its share of exhibitionists, as did another of his works involving members of the public, Clay and the Collective Body. For that installation, which involved giving up to 100 people at a time a 100-ton mass of clay to play with, they had two psychiatrists on standby in case things got out of hand (they were worried people might start copulating, for example, or urinating). In the end the only incident involved what Gormley described as a “bunch of crazy French people” who took all their clothes off and started behaving in “a slightly destructive way”.

This populist instinct, if that is what it is, might seem at odds with Gormley’s rather elitist and pious background. His father, who died in 1979, was a pharmaceuticals magnate. He was also a devout Catholic and disciplinarian who used to beat his seven children. The family home was a grand house in Hampstead, with a chauffeur and maids. School was Ampleforth, the equally grand public school in Yorkshire. After Cambridge, Gormley set off for India on the hippie trail. He was gone for nearly three years, contracted typhoid, studied meditation and thought about becoming a Buddhist monk. He then returned to the fold and trained at the Slade, where he met his wife (and the mother of his three children), the painter Vicken Parsons.

There was a bit of grit in his upbringing as well as privilege, then. His father, as he puts it, was “very controlling and very ambitious. There was a sense that whatever one did one wasn’t quite good enough, whether that was declining Latin verbs or excelling at sport.” It is poignant to think that his father didn’t live long enough to witness his youngest son’s achievements, and popularity.

Perhaps his most popular work was the one he exhibited in 2007, Event Horizon. Gormley figures began appearing on the rooftops around Waterloo Bridge. Pedestrians stopped and pointed at them, intrigued. Did he go and watch their reactions? “I did watch, from the balcony at the Hayward, but then very quickly they were assimilated, like a new lamp-post or a bit of street furniture would be assimilated.” When the show appeared in other capitals, however, the response was more alarming. In New York police were called after reports that the figures were “jumpers” about to throw themselves off the buildings. The same happened in Brazil earlier this year.

Gormley seems pleased that many of his sculptures will be around much longer than him. “Our time is provisional,” he says. “They are facts that are not going to go away, and that are… well, the ones in the tide-line at Crosby are changing the whole time, because they’re rusting, and getting covered in barnacles and all that, but on the whole they’re kind of enduring, in a way that we are not.” Since it’s his body that they’re modelled on, is it a form of immortality? He shakes his head. “I’m not interested in that at all. I’m simply trying to be practical. There’s no point in making another body when you have one already. The only way of doing that is to use the material that you’re closest to, the material that you live inside.” Tellingly, Gormley often talks about his sculptures as if they are real people. I know I find them strangely moving, but what about him? “I feel uncomfortable talking about this because all I know is it’s important to me that they have an authenticity that comes from a lived moment, and then, beyond that, I am aware that they are empty and nameless. They’re being, not doing, and they are waiting. They have time, we have consciousness, and they are waiting for the viewer’s thoughts and feelings.” He thinks the figures’ vulnerability and “uselessness” gives them a certain pathos. “This is the absolute antithesis of heroic sculpture,” he says.

Members of the public seemed to find Field for the British Isles, the 40,000 tiny terracotta models, affecting in a slightly different way, one which they couldn’t necessarily articulate. How would he describe that effect? “I’m not quite sure what the feeling is… yearning? Accusation? But those tiny figures are definitely looking for something, those eyes, those little becoming things. And I think there is a sense in which the work, because of the way it’s been made, is a reservoir for the unspoken thoughts and feelings of all of the makers.” Gormley is referring to the teams of volunteers who helped make the figures. He describes the end of their first day making these “little surrogate beings”; when the lights were turned off, they felt like they were abandoning them. “It was sort of magical, really,” he says. “They hadn’t been there in the morning, and then they were there in the evening. It felt odd to leave them there in the dark.”

As well as having an OBE, Gormley is both a Royal Academician and a trustee of the British Museum. Indeed he has to head off there now for a trustees’ dinner, he says. Will he change out of his T-shirt, or is he expected to look the bohemian artist part? He gives a rare laugh. “I think I might put a dark suit on, just so I blend in.” Does he consider himself part of the art establishment nowadays? “I’m not living in a Scottish croft.” Good answer. Does he ever feel misunderstood? He’s very articulate about his art, but he also clearly feels he has to explain it all the time, and perhaps justify it. “I feel terribly misunderstood, I feel terribly misunderstood.” (This is a speech quirk of his, by the way, the repeated phrases.)

I ask about his critics, most prominent among them being Brian Sewell, who has dismissed Gormley’s work as having “absolutely no artistic merit”. He has also said: “I find it rather ludicrous that a man approaching later middle age can think of nothing more than his own body as symbolising this, that and the other.” And one early review of Model called Gormley “A model of hype”. ‘Do such comments make him want to convert his critics, or does he think: “I’ll never change their attitude”?

“Well, I think critics are very useful. But I think that they, in a way, betray their position when they stop people looking for themselves. Judgment is very easy, but I think, on the whole, professional critics maybe see too much, and compare too much, and forget the joy of actually looking and contemplating for its own sake.” He begins rubbing his scalp, kneading it with his long fingers. “When criticism becomes an exercise of judgment over curiosity, and it blocks other people’s ability to exercise their own curiosity, I think that’s a real shame.” Maybe it is simply that the critics can’t quite forgive him for being popular. “I think there’s a big difference between popular and populist. I have no interest in being popular for its own sake. I am, however, interested in the idea that art should be everybody’s. Sadly, most modern art is about other art. And I think that’s a tragedy because it requires its own priesthood to interpret it.”

There is also the resentment caused by his commercial success to consider. Along with his rival Anish Kapoor, to whom he lost out in a bid to make “Boris’s Folly”, the artistic centrepiece for the Olympic Park, Gormley is this country’s most successful sculptor and it has clearly made him rich. This summer he paid £3 million for High House, a late-Georgian mansion set in 129 acres of parkland near Swaffham, Norfolk. He plans to spend a further £1.5 million restoring it. His creations sell for sizeable sums: a man-sized model used in the making of Angel of the North went for £2 million in 2008.

Does he ever have people taking stuff out of his bins, and thinking this must be worth something because it’s “an Antony Gormley”? “I don’t know. I wouldn’t know whether people have nicked things out of my bins or not.” Has he ever signed a napkin to pay for a meal, then? “No, I haven’t. I don’t, erm… I’m very happy to do the odd drawing for anybody, but I feel slightly uncomfortable about artists behaving like that, turning a scribble into a meal.” He seems a likeable if earnest man, a deep thinker who is pleasingly uncynical about his art. As a parting gift he presents me with a rather handsomely illustrated book about his work, and, on the principle that you never know what a well-placed signature might one day be worth, I ask him to sign it for me, which he does, with best wishes.