Horsing around: How Mark Wallinger finally won the hearts of the British public

It would be wrong to declare that "everybody" loves Mark Wallinger's horse, for one or two curmudgeons have already expressed their aesthetic reservations about the winning entry in the Ebbsfleet Landmark Project competition. But they are very much in the minority. There's a pretty fair wind behind the proposal that a 33 times life-size, naturalistic white stallion should be erected in Kent, at a cost of £2 million. What a credulous nation we are.

One person, at least, is not quite so carried away by what is routinely fêted as the concept's "perfect inevitability". The artist himself, unassuming in hiking boots, ill-fitting black trousers and a conservatively patterned cotton shirt, is treading more carefully. "It all seems pretty unreal still," Wallinger says, as he breaks for lunch, after a morning lecturing on The Russian Linesman, the touring exhibition he has curated. "I have had a moment or two of thinking ... this is so great. Great. Then I think, oh, I want to run away. This is what's going to define me, more than anything else, if it happens."

Unreal. If it happens. Wallinger – who was born in Chigwell, Essex, in 1959 and now lives in south London with the sculptor Anna Barriball – is right to be wary. His own experience as an artist has taught him that glorious serendipity, of the type that makes the concepts behind his horse seem so intellectually satisfying, is hard to come by. At the moment, the horse is being viewed as a wonderful symbol that ticks all the boxes. It has achieved success with graceful ease. The only snag is that it doesn't exist.

Wallinger, whose intellectual credentials are routinely bolstered by the information that he wrote a thesis on James Joyce, admits that the "Joycean idea of the epiphany" still has a huge appeal for him. "One needs those moments. They're blessings that sometimes come out of the accident of life. They make you think: 'I'm on the right road here'."

He pauses, and laughs at himself – which is something he does a lot. He admits that he thinks a great deal about connections and reversals, pleasing coincidences and odd conflations. "There's 25 years of dead ends in that lot," he says, rather mournfully, of his entire body of work, "and you only hear about the ones that come off."

Wallinger's 1996 work, Oxymoron, flutters presently by the Thames. The Union Jack is remade in the orange, green and white of the Irish tricolour, and the gag rests squarely on the fact that orange is the secondary colour that stands in opposition to primary blue, and green is the secondary colour that stands in opposite to primary red. The unarguable simplicity of those colourful facts turns what could be mistaken for a crude piece of agit-prop into a powerfully disinterested and witty observation.

His 2007 installation, State Britain, was a recreation of Brian Haw's banned protest in Parliament Square against the Iraq War. It was inspired by the convenient fact that the line that marked the edge of the one-mile exclusion zone brought into being to spare the blushes of Parliament, actually bisected the galleries at Tate Britain. The exhibit ran along the line, marking the point at which it would be legal in "state Britain" for Haw to reassemble the real thing. The unearthing of that detail was more telling than the painstaking reproduction involved in the rest of the work.

The current show, at London's Hayward Gallery, explores these sorts of moments, when intellectual, practical or physical lines are crossed. Artists range from Albrecht Dürer to Bruce Nauman and the exhibition includes various depictions of the Middle East and particularly Jerusalem. "You go to a few divided places and you see the United Nations insignia thing, and quickly you start to see UN as 'un', as if we can undo things ... when things get too messy and we wish we could take it all back, but we can't."

The maquette for the horse has been included in the show, and fits nicely with the exhibition's general concept. Here is a wholly successful work of public art, inserted strongly into the public consciousness before it has even left the drawing board. Wallinger is grateful that popular and critical reaction has suggested he is on "the right road" with the horse. Yet he seems uncomfortable, almost embarrassed, as he recounts the vast body of material that provides a cultural underpinning for the project.

"A lot of things came together very quickly. The chalk pits are where the cement industry originated really, and it's where the North Downs peter out into the Thames. So I was thinking North Downs ... Epsom Derby. Watling Street is there, and the most ubiquitous creature coming up and down there for millennia was the horse ... Chalk figures in the hillside, and then the particular history of Kent ... Saxon invaders had the white horse as their emblem ...

"And a thoroughbred is a kind of British invention, which has something of our history written on it. Imported Arab horses were crossed with indigenous mares then exported around the world ... and there is a blood line of male descent you can trace all the way back to ..."

Wallinger trails off, almost as if he is suspicious of the great mass of evidence he can marshal so effortlessly in favour of his project, and which has persuaded so many others so quickly that the horse is a worthy artistic endeavour. That's the trouble with the horse. It's so full of meaning that it is almost banal. Maybe that's why Wallinger's instinct dictates that it has to be enormous.

The horse is conceived as being as tall as Nelson's Column. It is trumpeted, correctly, if precipitately, as the most ambitious piece of public art that has ever been constructed in Britain. Some commentators have asked why it has to be so huge, complaining that it will be a monstrosity, and a blight on the countryside. Wallinger isn't at all bothered by any of this. "Fundamentally it's a very scarred, messy landscape round there, full of pylons and so on. So it needs something. It'll be standing there, in the very undemonstrative way, in a classic pose we can recognise from Stubbs and all the stud books."

For a few critics, the naturalism of the horse is a problem. They complain about an absence of mystery or transcendence, and suggest that it might end up looking like a giant child's toy. Again, though, Wallinger is relaxed. "In the end, it's not going to look like a real horse, but in a certain position, at a certain place, perhaps it will. I love the idea of what it will do to the scale and everything there, and there's this notionally sentient beast and its gaze ... and the interplay is another thing that happens there, so you know, we've got a responsibility to it, and it to us. Or something."

It isn't the weight of expectation that bothers me though. It's the weight. Amid all the discussion about the horse, the sheer impracticality of such a structure appears to have been forgotten. No doubt the technology exists to ensure that those improbably skinny legs can be given deep foundations and plenty of weight-bearing capacity. But getting a body up there? How's it going to happen?

Wallinger says that the body of the horse will be hollow. Really? That long neck? That great head? Where's the support? Isn't this structure fantastically ambitious? Isn't that £2 million, in the context of the challenges involved in construction, a suspiciously modest amount?

No one knows the answers to these questions. Wallinger says that a group of engineers is drawing up a feasibility study. But the group, at the moment, is "loose". He does admit it needs some kind of "breakthrough wonder in its manufacture" and says there have been "advances in tensile strength in concrete in recent years, so that might be a way of working".

Wallinger, rightly, is keen that the sculpture should be faced in "some kind of cement that is local" in order that it is in keeping with the cultural and physical landscape, and maintains its nod to Britain's ancient chalk horses. But he is aware as well that there are one or two problems with the upkeep of white concrete. He jokes that the horse might be "a bellwether for the health of our air" but also adds soberly that "there probably will have to be a stairway up the legs, in the interests of maintenance, and little flaps from which people will abseil out and give it a wash.

"At the moment the building spec is for 60 years, which is the standard spec for putting up a modern building. But the responsibility should be that you still want it around."

he horse has inevitably been compared to Antony Gormley's Angel of the North, that started out wreathed in controversy but has become unquestioningly adored. Yet the Angel of the North is just 20 metres high, less than half as tall as the proposed horse, and constructed entirely of steel, a material that the artist had long experience of working in. A more apposite comparison, unfortunately, is Thomas Heatherwick's ill-fated Manchester landmark The B of the Bang, a steel "explosion" celebrating Linford Christie's description of how quickly he reacted to a starting gun.

Latterly dubbed "The G of the Bang", because it was finally erected so late (and at £1.42 million, double its estimated cost), the sculpture could briefly claim to be the tallest in Britain. But when its spikes started falling out, it had to be fenced off in the interests of public safety. After some abortive attempts at fixing the problems, it was eventually conceded that it had to be dismantled. Legal action against the manufacturers followed.

Aspire, in Nottingham, is presently the tallest sculpture in Britain, at 56 metres. But it is a tall and narrow flute of a thing, of no enormous engineering consequence, and it still cost £800,000, donated by a private benefactor. There's no reason that I can see to believe that just one of the horse's legs should cost a great deal less than that. Wallinger tries not to fret about the money. So far, the costs have been met by three private companies: London and Continental railways, Land Securities, and Eurostar. He professes surprise that his proposal was not greeted with a little more of the "Shouldn't we be building hospitals, that kind of line" but points out that artists can't be choosers.

It is widely assumed that Wallinger is a super-rich artist, one of the BritArt crowd whose entrepreneurial attitudes moved the art world's centre of gravity to London, and generated much of the new wealth of the recent boom. Certainly, he benefited from that movement. Wallinger's early paintings were bought by Charles Saatchi, and exhibited in the Royal Academy's Sensation exhibition. He studied as a post-graduate at Goldsmith's, from which students assembled the groundbreaking Frieze exhibition, curated by Damien Hirst. He won the Turner Prize in 2007 – with his work State Britain – after a previously unsuccessful shortlisting.

But actually, as all that change was gearing up, Wallinger was working at a bookshop. "It was a different climate. I left art school in 1981 – there was the John Moores Painting Prize, there were a couple of Cork Street Galleries, there wasn't an immediate future that seemed to beckon out there. So all that ... came as something of a shock.

"My first show was in 1986. It pre-dated the Frieze thing. I'm slightly older than those people. But it was a welcome thing. When I was at art school if you wanted to do anything figurative you were put in the eccentrics room ... so you had to find your own sustenance back then. At that point I just felt glad I had a part-time job in the evenings and Saturdays which meant that I could work during the day. The money thing, for most artists, is still quite bumpy."

It is for this reason that Wallinger has been dedicated for some years to pursuing public projects that come with plenty of money attached. He says he has entered nine competitions like the Ebbsfleet one, including the competition that was won by B of the Bang.

There can be no doubt that the energy of BritArt itself fostered the climate in which so much money became available to make public art, also stimulating a general culture in which people were no longer suspicious of big artistic projects but instead quite excited by them.

It seems a shame really that Wallinger should have got his big commission just as all that extravagant investment in art is grinding to a halt. Perhaps his horse will be built, a romantic tribute to human ingenuity for its own sake. But if it is constructed, the likelihood that it really will stand at 50 metres cannot be great. Even if it remains just a bright idea, the horse will stand for something. Unfortunately, and as far as Wallinger is concerned quite undeservedly, that something may be the collective folly of a time when so many people decided that they could be an art critic, and so few decided that maybe they ought to be an engineer.

The Russian Linesman is at the Hayward Gallery, London SE1, to 4 May, 0871 663 2500