It's 11am at the Royal Academy in London, and the joint is jumping. It's Buyers' Day at the Summer Exhibition ahead of its opening today, and a multitude of people who bought RA exhibits some time in the past are here for an early preview of an event that has been a fixture on the social calendar since 1769.
While would-be purchasers enjoy glasses of Pimms and contemplate six gorgeous abstracts by 80-year-old Gillian Ayres, elsewhere in the building, dozens of children stand dumb-founded in front of an intimidating King Kong sculpture, fashioned by David Mach entirely from coat hangers, or examine (in "Crash Willy" by Yinka Shonibare) the spectacle of a hilariously smashed-up Model T Ford and its decapitated driver in his country tweeds.
Approximately three miles away, the man who's overseen this arty free-for-all for the last six years is keeping well out of it. Sir Nicholas Grimshaw, President of the RA and world-class architect, has more weighty things on his mind. He is chairing a meeting about some building work at St Thomas's Hospital. As the chap behind a few hundred major building projects of jaw-dropping eclecticism, he is always in demand, always internationally busy. But not too busy, I notice, to contribute a couple of artworks to the Summer Exhibition.
There they are, in the Weston room: two engravings, modestly priced at £250 each. One is called Archipelago 1, the other Estuary III. Both are carefully, even proudly, dated from two days in May 2010. This means that, less than a month ago, the hardest-working architect in the UK took the afternoon off to design an estuary and an archipelago. Why?
He laughs, rather shyly. "I was asked to. Eileen Cooper and Simon [Chambers] who are on this year's hanging committee, said, 'Why don't you give it a go? We'd love to have you [in the exhibition.]' I said 'I can't, I'm far too busy'. But then I thought, you have to have room in your life to change gear, and try something different. I've always been obsessed with maps, and I'm fascinated by Googlemaps – you get the most amazing colours on them. So I got a Googlemap of Wells Next-the-Sea on the north Norfolk coast, where we've got an old barn, and I focussed on it and started etching. Eileen was a terrific teacher. I did it in an afternoon."
He sounds exultant. One can only wonder how he felt in the past when one of his epic projects was completed. Like the Eden Project in Cornwall, the world's largest greenhouse with its SF cluster of biodomes. Or the Fair Trade Hall in Frankfurt, with its steel ventilation shafts like Darth Vader helmets. Or Oxford Ice Rink, Bilbao Bus Station, Terminal 3 Heathrow, the Financial Times's printworks, the Sainsbury's supermarket in Camden Town, the Rolls-Royce manufacturing plant, or the futuristic National Space Centre in Leicester. To all, he has applied his key principles of "structure, order, detail and flexibility" to produce miracles of elegance, coherence and human scale. He has not, so far, punctuated the London skyline with a Gherkin building or a Lloyds Bank skyscraper; he seems to favour shorter and wider structures, from the international terminal at Waterloo Station to the grandstand at Lord's cricket ground.
What does a professional architect bring to a venerable academy of painters and sculptors? Does the architect have a different sensibility from artists, who work mostly in two dimensions and by themselves? "I like to think I'm plugged into the art world," he says. "My father-in-law was John Russell, the Times's art critic for 25 years. My mother and grandmother were painters – they used to get work into the Academy from time to time.
"My sister is a very good photographer, and my older sister, now in Australia, went to the Royal College of Art. So I have a certain background."
Indeed. Born in Hove, East Sussex, in 1939, he's a young-looking 70 in a cream suit and Hockney-esque perspex glasses. His manner is friendly but diffident. One can easily imagine the pre-teen Nick in his bedroom, patiently constructing the Meccano sets which first inspired his interest in engineering.
Grimshaw presides over the famous "hanging committee" which selects 1,200-odd exhibits for the summer display from the submissions sent by famous artists and members of the public alike. How does the judging work? "I chair the selection committee for all four or five days as 11,500 pictures go past. Each picture is thumped down on a stool in the middle of the room, and we put our hands up if we like it. It's amazing how much consensus you get. Every picture is carefully looked at, and some inspire long discussions. People who think the selection is random are quite wrong."
Does he welcome all forms and techniques under the heading of "art"? Video installations? "Oh yes, there's a wonderful piece by Bill Viola." Conceptual art? "Yes, we put it under the heading of 'sculpture'." Did he have to re-think the old criteria by which artists become Royal Academicians? "In the earliest days, painters, printmakers and engravers were all lumped together as RAs, along with sculptors and architects. We have to stretch the categories sometimes. A new member called Tacita Dean mainly makes films, but she started as a painter, so we slipped her in as one." His eyes gleam. "I'd personally like to see some members coming in whose work is completely electronic. It's the age we live in, isn't it?"
Tracey Emin became a Royal Academician on Grimshaw's watch. How would he define her achievement to sceptics? "I think she draws and paints beautifully, in an extraordinary kind of way, if you really look. To some people her works look throwaway – but there's a huge amount of care and effort in it. She's also played a really good role in the Academy. She's been on committee meetings, she's going to be on the Council next year, she talks to other members, loves being part of the community." So you made her an RA for being sociable? "It's important, being an ambassador. She's done wonders for the place. It's been very good for us."
He admits to being impressed by Jake and Dinos Chapman ("I think the Chapmans are terrific. I'd love to see them elected as RAs") but discerns "a huge amount of the emperor's new clothes" about what goes on in Charles Saatchi-land. "You have to look at the individual artists and their work carefully and shouldn't ever take it en masse."
I ask him about the Chelsea Barracks debacle last summer. It was a nasty moment for modern architecture. The Qatari royal family own the old army site and were looking for someone to mastermind a multi-billion-pound housing project. Days before, Richard Rogers – the visionary behind the Beaubourg centre in Paris and the Lloyds building in London – expected to receive planning permission to proceed, he was told the Qataris wouldn't be needing him. It was, it transpired, the result of an intervention by Prince Charles, who has been a thorn in Lord Rogers's side since the late 1980s. He had apparently contacted the Qatari royals – prince to prince – and asked them not to choose Rogers. Was the Prince wrong to step in? Should Rogers always be allowed to have his own way?
"It's a difficult one," says Grimshaw, clearly not keen on being dragged into a dispute. "The whole thing stemmed for the fact that the Qataris paid too much for the site, and had to get a huge density [of building] on it. I think Rogers is a very good architect but he was constrained by having to get this enormous amount of accommodation on site. Everyone felt it was too much. The Qataris should have gone back to Rogers and said, 'Look we've overdone the density – can you have another go at it?'"
And Prince Charles's role? Grimshaw considers. "I just don't think it's right. Prince Charles has to make his mind up about what he wants to be. He can write to the Qatari prince to say, 'Look, I don't like your scheme,' which anyone can do over the garden fence if they want to. But I don't think that's the right role for him, if he's also an employee of the British public. We have a minister of planning for doing that. We have the most democratic planning process in the world, and I don't think it should be interfered with in that way. Charles is not appointed to be our adviser on what we should or shouldn't be looking at. He needs to make up his mind."
Grimshaw has not been shy, in the past, of criticising government for poor choices of architects in commissioning public building works. In a speech in summer 2006, he said: "Some of the most awful buildings around have been put up during the life of this [New Labour] administration." Such as? "It was in connection with some schools, hospitals and university-type buildings which were publicly financed. People would say, 'Oh it's only a hospital, it's going to happen anyway, it's got finance, it doesn't need to have proper critical faculties applied to it'. The government didn't care, because they were getting the building built and they had 30 years to pay for it. They were just delighted to get the thing done."
What should the government's priorities be then? Grimshaw grew suddenly emphatic. "It's quality, quality and quality they should be looking for, and nothing else. It's nothing to do with money. Sometimes a utility building is terrifically challenging for an architect. It's not to do with cost or fees. An architect's fees are a drop in the ocean – the difference between what one company might quote and what another might quote is peanuts. They should just decide on quality. They need to get the right people on panels to make the right decisions. But they don't take it seriously enough."
By "they" does he mean the Environment secretary? "Exactly."
Grimshaw gleefully tells a story about a party in Downing Street during Tony Blair's rule. "It was a party for designers and architects and there was a hilarious moment. He stood up on a little box in the room – everyone was holding their drinks – and said, 'I've been thinking hard about design and architecture, and an amazing thought occurred to me. A good building doesn't cost any more than a bad building'. And we all thought, 'for Gawd's sake, he's finally got it. A bad building costs exactly the same as a good building'. He said, 'We really,really shouldn't build bad buildings,' and we thought, 'Yes, you're definitely getting there, prime minister'.
"The government should put huge amounts of money and time into choosing [an architectural partner.] They shouldn't do it casually or sloppily. There's a lot of very good young architectural firms out there. We'd obviously like a slice of the action ourselves, we've got mouths to feed. But we're perfectly happy to see young architects on shortlists. The government needs to take it seriously, to see that the public realm of architecture, that people have to look at, is very important. In this age of austerity we're about to enter into, it's even more important that they concentrate on quality and don't just choose the cheapest quote and say, there's nothing we can do. I don't think architecture and the arts and culture get nearly enough time and attention from the government. I really don't."
The Royal Academy Summer Exhibition opens today at Burlington House, London W1 and runs until 22 August