Michael and Patty Hopkins's Hampstead house has become a legend in its short lifetime. It was built in 1976, but still passers-by gape, tourists snap and architectural students come to worship and make notes.
For years, they were the hi-tech couple, who loved factory-made components and modern design, well respected by their peers, but hardly known outside, considered not as racy as Richard Rogers or as famous as Norman Foster. In the last 10 years they have moved more mainstream, gobbling up some of the nation's prime commissions - at Lord's cricket ground, Glyndebourne Opera House, the Inland Revenue HQ in Nottingham and the New Parliamentary Building for the House of Commons, projects costing up to pounds 60m a time.
Last month they were awarded the Royal Gold Medal for Architecture, the world's number one architectural accolade. The Hopkinses have won it together, the first British couple to do so. Only one other woman has won it so far - and she was sharing.
They were at their table, drawing away. They'd seen me, through the glass acres, but left me to find my own way in. They did have a bell on a wire, back in 1976, but it broke and was never replaced. 'I never worked out how to fix a doorbell through glass,' said Michael.
The house is in one of Hampstead's most affluent Georgian rows - but they have never been burgled. Burglars probably find it too intimidating, crossing the drawbridge, being watched from inside. And there are no little windows to force open, just massive sheets of glass. 'It would be like a bomb explosion if you broke one of them,' said Patty.
They work side by side, at home or at the firm's offices in Marylebone. How many staff have they now? 'Seventy,' said Patty. 'Fifty-five,' said Michael. 'Seventy,' repeated Patty, 'counting all the admin staff.' 'That's rubbish,' said Michael.
Oh, I do love to hear long-married couples squabbling over petty things. So reassuring. They've done it all their life. Never on anything that matters. Just boring facts and figures or who's responsible for certain things. Their children used to say they'd get on much better if they didn't work together. But that's mostly how it's always been.
Michael is 58, tall, rather academic-looking, round specs, thick head of hair. He went to Sherborne School. 'I wasn't the academic type so the school wasn't much interested in me. I got only a few O-levels, about the same as John Major, but I loved school. I spent a lot of time cycling round the country, looking at churches.' He left at 17, before A-levels, as his father, a builder, was having a hard time financially.
'My mother decided when I was 14 I would be an architect, and my younger brother a doctor. Both came true.' He spent two years at Bournemouth College of Art, on an architectural course, but it didn't count as a proper qualification. So for the next five years he worked in various offices, as an unqualified architect. At the age of 24 he decided to get qualified, and got into the Architectural Association. 'I got an LCC grant. My father could not have afforded it otherwise.' Enter Patty.
She is 51, slim, elegantly if rather formally dressed, with Audrey Hepburn hair. She comes from Staffordshire, and her grandfather was an architect. She went to Wycombe Abbey school, sailed through O-levels, and was on course for university when a visiting lecturer inspired her to be an architect. So at 17, she entered the AA. 'Much too young, really.' There were 50 students on her year - only five of them women. (Today, it's about 50-50.)
'I first saw Michael when he walked into the cafe looking sophisticated, smoking a cigarette, wearing tight jeans and a washed-out leather jacket. He looks desirable, so I thought.'
'It was Patty's nice knees I noticed first. She was the prettiest girl there.' Out of five? Not much of a compliment. 'Oh no, but she was. She laughed a lot and seemed jolly. She still does. She used to hang around my flat a lot.'
'What a lie,' said Patty. 'You used to hang around me, when I was working.'
He proposed marriage one month after they met. A month later she agreed. 'I was rather a weed in those days.'
'It was the only way to live together, getting married,' said Michael. Almost immediately they had a daughter, followed by a second, while Patty was still a student. She took a year off and didn't qualify until 1968, when she was 25.
In their student days, who was thought most likely to succeed? 'I'm the clever one,' said Patty. 'I mean academically. I'm quicker, but Michael is the one with the talent. He's also got annoying persistence, and he's usually irritatingly right.'
She went to find a letter, one of many congratulating them on the Gold Medal. It was from the architect John Winter, once Michael's tutor, recalling that he'd been 'the most awkward and subversive student at the AA'. True? 'Well I was a mature student, and thought I knew it all.'
Michael's early jobs were on big New Town housing projects. What went wrong with so much of the Sixties' housing?
'You have to remember in those days we all felt very idealistic,' said Patty. 'We honestly did think we were improving people's lives. It was part of the post-war clean sweep, which we all shared - architects, planners, local authorities. What happened was the scale was too big, and we didn't realise how much maintenance, guarding and policing was needed. English people didn't take to them, anyway. In Europe, especially France, they have a history of living in apartment blocks.'
From 1969-75 Michael was in partnership with Norman Foster, till he decided to break away. Some row? 'No, there just wasn't room for two chiefs.'
Patty, all this time, had been working from home, balancing au pairs and three children. In 1976, they decided to set up Michael Hopkins and Partners, just the two of them, both working from home. Their Hampstead glass house proved a vital selling point in the first few years. Clients loved coming to see them.
'Ah, those days have all gone,' said Patty. 'At one time the client did most of the work. He'd visit the offices of, say, six architects, talk to them, see their work, then decide which one to appoint. Now it's all competitions, which is very expensive and time-consuming.'
So far, they haven't built abroad. 'I don't know why,' said Michael. 'Perhaps we're not good at publicity or drawing attention to ourselves. We've flourished quietly in our patch.'
After a lifetime of glass, concrete and steel, they discovered something unusual in 1984. Brick. 'A happy accident,' says Patty. 'We found on the Lord's site we had inherited some brick arches. We decided to use them - and built another 20. Since then, they've incorporated quite a lot of brick and stone, at Glyndebourne and the House of Commons, though still retaining a basic Modernist approach. The Prince of Wales is now one of their fans - at least he likes their Lord's stand. Isn't that the kiss of death for a modern architect? 'It's always nice to be appreciated.'
I wondered which were their favourites. 'I like them all,' said Michael. 'We have a track record in likeable buildings. We haven't done a lulu yet.' Patty did pick a favourite - Bedfont Lakes, near Heathrow, as it is often overlooked.
They will drive miles out of their way just to have a look at one of their old buildings. 'They are like our children. You remember all the difficulties in bringing them up.'
Only one of their three children is still at home - Joel, aged 23. Patty says she always put them first when they were young. 'My career has been interrupted and muddled while I concentrated on the kids. One of us had to do it, and it obviously had to be me.' Because society brainwashed you? 'Probably, but I enjoyed it.'
Now Patty works full-time, one of the firm's five partners. Who's the boss? 'Oh he is. He is there at the beginning of every job, starting them off, then I or one of the other partners get involved. It's good to have one person standing back, looking at the whole, acting as sounding board. I'll always consult him on anything important . . .'
'I'd be jolly cross if you didn't,' said Michael.
Patty is not in Who's Who, nor has she personally shared many of the other plaudits that Michael has received in recent years, but the Gold Medal is joint. This is due, they think, to their Glyndebourne job, where Patty had a major role. Has she suffered from sexism? 'When I was younger, older men would be rather patronising. You still find certain clients uncomfortable with women architects, but I can't say it exercises me. I'm not a feminist. I'm an architect, trying to concentrate on my work.'
As a couple they contribute different qualities. She is the optimist, he is the worrier. 'We have enough for this year,' he said, 'but I am worried about next year. Nothing's coming in. The recession is still with us.'
'Don't be silly,' said Patty. 'You've always thought like that. Anyway, better buildings get built in leaner times.'
Patty took me round the house. It appears one-storey from the street, very low, like a glass box sinking below the trees, but it's actually two storeys, very spacious, with a large lawn at the rear. Planning permission was easy, granted in six weeks, perhaps partly because there existed permission for two four-storey houses, which would have been four times their size. They paid pounds 30,000 for the site, and pounds 20,000 to build.
The steel bits - ceiling struts and pillars - are painted bright blue. All the fitted carpets are grey. There are no interior walls, except around the two bathrooms. Elsewhere, venetian blinds act as dividers. Over the years the space has been rearranged, for their children, then as workplaces, boardroom, then back to living quarters.
They still love it, and plan never to leave. 'We were brought up in brick-and-plaster buildings, as most people were, and although we enjoy brick now more than we did, the aesthetics of glass and steel still excite. We've found that old people and young people immediately love this house. Only the middle-aged get a bit worried.'
Inside, you obviously have to get used to living a public life with one's family, but outsiders can't see in, despite the glass. You also have to be very tidy. I remarked on the noise of a lavatory chain being pulled downstairs, something you wouldn't hear in a normal house with rooms and walls and stuff. Patty said she didn't hear it.
Last month, in a news article about their Gold Medal, the Daily Telegraph printed a photograph of the house - upside down. That sort of thing used to happen with Picassos. It shows what they have created - a piece of modern art.