Architect Jean Nouvel has designs on London

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Nouvel is up there with Foster and Rogers; he's designed towering buildings for Barcelona, Paris and Abu Dhabi, but only now, aged 64, is he about to make his mark on London. Zaha Hadid, Frank Gehry, Daniel Libeskind and Oscar Niemeyer have all previously designed the temporary structure in Hyde Park used for parties (including the Serpentine Gallery's glittering annual fundraiser) banqueting, public sleepovers and, this year, ping pong. I want it to be a popular pavilion if possible,' says Nouvel. Winner in 2008 of the Pritzker Prize and fêted inter-nationally, his fingerprints are on almost every major city apart from London (the Serpentine always picks architects at the top of their game). But he is about to be well-known here for One New Change, a sinuous, shiny shopping plaza overlooking St Paul's Cathedral, due to open in October. It does not have the royal seal of approval. Bête noire of Prince Charles, eh? Ha ha ha!' he laughs, referencing the row that erupted when it emerged that in 2005 the Prince wrote a private letter to the site's developers, suggesting they deselect Nouvel in favour of a traditionalist architect who would allow St Paul's to shine brightly'. Today Nouvel seems part amused by this, part angered, calling the Prince's pet project, the mock-classical Paternoster Square development on the other side of St Paul's, totally a disaster. An homage [to another architectural style] is always a disaster. All Prince Charles wants, I think, is homage, is' he says with disgust, architecture d'accompagnement.' Nouvel's own design will be complementary' to Wren – You don't want to pick a fight with St Paul's' – but very much of its time. Before it opens, we have a Nouvel taster in the form of his Serpentine folly, a scarlet cubist fantasy that will stay in Hyde Park for three months.

A charismatic man who bears a striking resemblance to Dr Evil, Nouvel keeps his staff on their toes. His atelier in the 11th arrondissement is a light, airy place full of designers working under red or black Anglepoise lamps, but before the man himself appears his staff are visibly tense, checking that the design models and bright red polycarbonate samples are all arranged just so. Then he arrives in an aromatic cloud of Pour Un Homme de Caron, wearing his habitual Yamamoto outfit, ink-black from head-to-toe and dressy as a priest's soutane. Summering in Nice, he wears all white.

It's easy to assume starchitect' means an architect so starry they squiggle a gesture over the landscape and then send their team of engineers to do the rest, but Nouvel is hugely enthusiastic about his pavilion, which is due to be surrounded by green shrubs dotted with red – Chillies, red berries, stro-awberries,' his accent makes the word into jam, as if they are being grown by a woman or gardener who loves her garden, I want, oh! these little pleasures. I want a playground in 'yde Park.' Is it intended as an antidote to current economic anxiety? No, it is not really useful, it is only for pleasure But then pleasure is useful, no?'

Jean Nouvel can bring paradoxes out of a hat; you can see why he was friends with Jean Baudrillard, the riddling postmodern philosopher of hyperreality. Transparencies of Baudrillard's photographs of Parisian park life will be on display in the pavilion, recalling the walks and talks they had together in the forest of Fontainebleau; the red awnings are copies of those outside Nouvel's favourite Trocadéro brasserie. Red is a colour he has deployed across the world, from the high-shine burgundy of his Museo Nacional Centro de Arte Reina Sofia in Madrid (2005), to the crimson glow of his Lyon Opera House (1993). But he doesn't think of the similarities between his buildings so much as the differences.

I have a philosophy of specificity,' he says. I fight always against generic architecture, which is really the worst. I like to research a lot the particular situation where the building will be; its context. So in the case of Lyon, for example, I play with red lights because it's a polemical question in Lyon because it's the symbol of a prostitute's house. In London it's different' Quick as a flash, a minion shows a mood board featuring red London icons: a bus, a letterbox, a phone box. Not so fast!' says Nouvel in French as they click to the next slide. You'll give me a headache!'

Over lunch I dig a little deeper. My first memory of red?' He sets down his glass of wine – appropriately, a rich red Graves from Bordeaux – and whistles dreamily, thinking back to Lot-et-Garonne in the southwest of France, where he was born to teachers Roger and Renée in 1945. We had cherry trees when I was a kid, and we had a game: who can catch the cherries. Yes, beautiful! And strawberries, in the garden. So my first idea of red is probably Gourmandise. Pleasure.'

He wanted to become an artist: But for my parents that was too risky, they prefer I become an engineer. So I propose architecture When I was a student there was a big discussion and fight about this. An affectionate fight.' Gaining entry to the Ecole des Beaux-Arts was a struggle: I was very lucky because I failed the first time in Bordeaux but then a year later I succeed number one.' By which he means he came first in the country.

At university during the student riots of 1968, he was deeply affected by structuralism – hence his maxim that context is everything – and politically he did his bit by co-founding the Syndicat de l'Architecture (architects' union). He is proud of having designed council flats as loft-style apartments rather than punitively dowdy homes: It proved what you could do for the same price and it caused a big fight.' He is still full of the urgency of improving les zones sensibles, the poverty-ridden suburbs of major French cities, and regrets what he sees as a governmental lack of interest. His first employer, architect Claude Parent, was a mentor. When I left his office he said, "I will give you one or two things, some shopping centres."' But Nouvel's breakthrough was one of Mitterrand's grands projets, L'Institut du Monde Arabe, in 1981. Still a serene success, it stands on the Left Bank of the Seine, its light-sensitive lattice portholes referencing Arabic design, as well as the rose windows of nearby Notre Dame. If Nouvel has no trademark style it is because he is sensitive to each building's surroundings.

Other triumphs include the Torre Agbar in Barcelona, despite the fact that it looks highly similar to Foster's Gherkin, an observation he brushes away: Mine is based on the traditional shape of Catalan architects, of Gaudi's pinnacles. I think Norman's building is more Gothic. They have a different meaning.' Ask which of his buildings is his favourite and he comes down hard: There is no question more stupid. We cannot classify. Two very good books, two movies, one is better than the other? To compare, it's an illness of the 20th century.'

Nouvel has had more career disappointments than most, declaring, I'm a world champion of lost competitions.' All architects win and lose commissions, but Nouvel has more than 100 unbuilt dreams in his portfolio. Sometimes even the competitions he wins remain unrealised, notably the Tour Sans Fins at La Défense in Paris (designed in 1988), a tower without ends' that was to appear sprung from the centre of the earth' and transparent at the top', a vision judged too ambitious for recession-hit early 1990s Paris. For many, many years I lost so many competitions Then I did less, so of course I win more. Last year I think was the right ratio at last.' Recent commissions include the Louvre in Abu Dhabi (due to resemble a levitating doily) and the National Museum of Qatar (a modernist caravanserai). Anyway, it means I stay more young!'

He does look young for 64, having recently taken himself in hand. Since many months now I do a bit of sport every day, because that was very necessary.' He draws what would have been a Falstaffian tum. I like to swim. Initially it was not pleasure but now it becomes a little bit of pleasure.'

Twice married, with a complex love life, he is said to have recently been reunited with his second wife after an affair with a fellow architect Mia Hägg. He has two sons from his first marriage to Odile Fillion, a film-maker, and by his second wife Catherine Richard, a theatre producer, a 15-year-old daughter. One son is about to make him a grandfather for the first time!'

London he finds mystérieuse, wide-ranging, hard to understand. Unlike Paris it's not structured.' Still, he is now setting up stall opposite St Paul's Cathedral, despite the protestations of Prince Charles. With some indignation, he defends his modernist agenda: In a historic neighbourhood it's very important to have a fresh testimony of each different epoch, not false buildings, false columns, false scale.' He adds: And if you make a big mistake, which people can do sometimes, you demolish it.'