From an insignificant cable-clip to the stately, undulating lakeside glass façade of this complex, it is all like this. Talk to Ron Dennis, and immediately you are into information overload about the how, why and wherefore of one of the most beautiful, spotless factories I have ever seen. "This is driven by attention to detail," he explains, needlessly. "It was seven years of my life".

Seven years of being on site at 5.30 in the morning, sometimes. He is possibly the only client in existence who can outdo the Foster office for sheer doggedness when it comes to getting a building right. David Nelson, Foster's right-hand-man in charge of the project and himself an industrial designer by training, still marvels at the extraordinary amount of time he spent with Dennis, discussing the tiniest minutiae of what is, after all, just a motor works. "That kind of thinking is what you don't normally get in architecture," says Nelson in wonderment. "Their standards are so high. Compared to manufacturing industry at this level, the construction industry is miles apart, very crude in comparison."

This microscopic focus is no doubt what makes the McLaren Formula 1 motor racing team so successful. It explains why Mercedes trusts Dennis to make their top-of-the-range gullwing-door sports car, in this very building. It explains why he can sell his electronics technologies to other racing teams. Dennis - a tanned, fit man of 58, who you'll catch a glimpse of on TV most Grand Prix weekends, studying the telemetry data from his cars out on the track - is one hell of a businessman. This building, which cost well over £100m even without the incredibly costly equipment inside it, is a long-term investment.

It does not look anything like a factory. As you arrive and drive slowly through the landscaped grounds along the VIP approach route round the lake, what you see is more like the grand corporate headquarters of an international conglomerate, crossed with what could be a dream of a 21st century country house. Inside I looked and I looked, and not only could I find no spot of oil or muck anywhere - even in the bays where the Formula 1 cars of Kimi Raikonnen and Juan Pablo Montoya are stabled - but I could not find even a speck of dust. Even a wrecked carbon-fibre car chassis, the result of a fearsome high-speed crash, is presented almost as if it were one of the many pieces of abstract sculpture that are dotted around the building.

I have come to see this building for two reasons. One is that I love factories, yet very few factories, especially in the UK, get much in the way of design attention. The other is that I know how misleading the perfect architectural photos of such places, usually taken at the moment of immaculate completion, can be. The reality is that a lot of buildings have dodgy details from the outset, and then proceed to get shabby and flaky pretty quickly. So I have come to see this factory after a year of operation. That's a lot of cars and materials and equipment and people going in and out. It's going to be a bit of a mess by now, isn't it?

"You'll find it meticulously maintained," says a passing company suit, slightly reprovingly. "We're pretty fussy in Formula 1". Fussy? I should say. This verges on obsessive-compulsive behaviour. A workman appears to be polishing light fittings in the floor. The place glimmers. There is a deep background world of autoclaves and spray booths and mysterious underwater cutting equipment and a huge, silent, wind tunnel. There is a Thunderbirds-style main public boulevard running in a sinuous curve along the lakeside, where receptionists for the various divisions of the company sit up on circular platforms like flying saucers. It is all kept squeaky clean, back or front of house. I did find a slightly scratched door in the basement where trolleys are pushed through. Ron Dennis apologises for this, and explains that it will be fixed shortly.

McLaren is a big business, employing around 1,000 people in this building. And of course what it does is high-value. This, if anything is, is the future of British manufacturing: highly advanced technologies producing a relatively small number of state-of-the-art, constantly-evolving products that nobody else can possibly copy or make more cheaply in time. McLaren can design and make a new part and fly it out to a racetrack virtually overnight. This is as far removed from metal-bashing as it is possible to imagine.

Cars are being made by people in black T-shirts. Boffins are designing stuff on computers. Sheets of carbon fibre are laid into moulds for ultra-strong and light components. Classic racing cars stand in echelon in the boulevard. A 50% scale model Formula 1 car is being prepared for the wind tunnel. Fat carp frolic in the warm waters of the lake outside, which cools the whole plant. Over everything there is a respectful hush. Dennis is talking about what he calls "languages" of varieties of white paint, or of shadow-gaps. He spirals into abstraction, and then comes back to earth. "It has a Zen-like quality," he says. And even he sounds impressed.