It's hard to imagine by what caprice of evolution this walking embodiment of an arty English public schoolboy turned out to be not a travel writer like Colin Thubron or Bruce Chatwin (both of whom he resembles), but a scientist. It goes against nature to find him sitting in his barn-like HQ in Malmesbury, Wiltshire, theatrically clad in a lilac chemise and talking about cyclonic filtration. It's weird to see such a sensitive chap pulling out the hose attachment like a light sabre.
"The thing is, I enjoy trying new ideas, experiments and tests, and it's what I do every day. It just happens that, for 26 years, I've been doing it with vacuum cleaners. I suppose if I were a stylist, designing cleaners for 26 years might be boring - but what I'm about is improving performance and developing technology. That's what drives me."
Gods, as Homer said, make their own importance. And Dyson has an Olympic profile in British business circles. He is wildly successful. His personal fortune is some £800m. His products sell in 37 countries. He's a CBE. His DC01, the cleaner that sucks like a sex-crazed limpet and doesn't bother with dust-bags, has taken over the world.
This year, Dyson overtook Hoover to become the biggest vacuum-maker in America, with 20.7 per cent of the market against Hoover's 15.6. His "contrarotator" washing machine, with its purple-grey livery, is a huge success, with its complex helical cycles. He also invented the Ballbarrow - a wheelbarrow with an orange ball instead of a wheel - the Sea Truck, and the four-wheel-drive wheelchair....
It's not surprising that such a keen maker of things should be hot on the history of discovery. As co-editor of The Mammoth Book of Great Inventions (Robinson, £9.99), he examined how everything got started, from flint tools and fire to Viagra and cloning. The first dust-busting device, we learn, came out in 1901, developed by one Hubert Booth after he inspected a new American gadget for removing dust from upholstery. (The device blew the dust up into the air. Wouldn't it be better, thought Booth, if it sucked instead?)
What's amazing, however, is the number of inventions around at the same time. Many things that define the 20th century appeared in its first five years - human flight, plastic, radar, nylon, broadcasting, air conditioning, colour film, washing machines and the vacuum diode that gave us radio, television, amplifiers and digital computers.
Does Dyson notice the same prodigality of invention today? "No, but there's a different type of invention around. The wonderful thing about the Victorian era is that there was so much to invent. Except for computers, they had all the tools we have - machines and lathes, engineering works - but nothing had been done. It was a completely open field. There was a flurry of activity until the controller of the US Patents Office said: 'We may as well shut the office, because everything's been invented.'
"What we have today is a series of refinements, which are in many ways harder than the original invention. The breakthrough, the quantum leap, may look extraordinary, but refining it is more complex. It's what the Japanese have taught us."
Dyson chuckles admiringly about the Japanese application of ideas. "I love that story about Akio Morita [boss of Sony in the 1970s] coming up with the Walkman by not listening to his marketing department. They said: 'It's got to record. You can't sell something that just transmits.' But Morita had the balls to say, 'No, I just want something that plays, so I can listen to my favourite music when I'm in an aeroplane.' I like that."
For years, Dyson has been a one-man crusader for manufacturing industry, which he sees as a lost heritage of British society, a dwindling, unloved and disregarded sector of business, a dirty secret. Surely, I say, factories got a bad press ever since Blake called them "dark Satanic mills" in "Jerusalem", 200 years ago?
"Yes, that has coloured everyone's view of manufacture; that it's dark and messy and exploitative. The Victorian aristocracy and intelligentsia didn't adopt manufacturing as something we should be interested in. I'm 58, and when I was young, the whole idea of getting an education was so that you didn't go into a factory. You went into the Foreign Office and got a good job. Now we have a serious problem, because only 14 per cent of our GDP is from manufacturing, while most of the world's production is still heavy engineering, and demand for it grows at a faster rate than the demand for software."
The trouble, he thinks, is that British people revel in their ignorance of technology. "There's an inverted snobbery, that people don't know how to change a light-bulb or fix their car. They boast about not being able, when it should be a source of shame."
His company does its bit to further an interest in tinkering. "Manufactured objects have become so sophisticated, it's impossible to open them up and try to fix them. But our products you can take to bits and put back together. We send vacuum cleaners to schools. The children take them apart, reassemble them, ship the box back to us; we mend it and send it to another school."
Dyson's plea for the dignity of the assembly line had a setback in 2002, when he shifted his own to Malaysia, leaving 800 workers laid off at home. What precipitated his action was being refused planning permission to extend his plant by a few hundred yards. Such pettiness, combined with growing labour costs and the fact that his mechanical supplies were already coming from the Far East, spurred him to go. It worked out commercially - production costs went down by a third, and the company now employs 1,200 people at the Wiltshire HQ - but the incident gave Dyson the reputation of having a ruthless streak.
His cleaners and machines are still assembled in Malaysia, while his huge Malmesbury plant is populated by earnest thirtysomethings tapping laptops. "They're the research and development department. We have 350 people here, scientists, lab staff, test riggers - you need a big space for it."
Dyson believes passionately in R&D, spending £40m a year on it. Did it sometimes seem a waste of money? "There are always mistakes, or you develop a product then realise it's not good enough to launch. Whether 'waste' is the right word, though - you learn an awful lot about engineering or technology from everything you do. Some mistakes come good, some you don't - but that's part of the fun."
Dyson is writing a series of articles for the Independent entitled "How to Be Different". How different had he been when young? "I suppose I embraced different-ness at school, if playing the bassoon shows an urge to be different. That and long-distance running," he says. "And I felt different because my dad had died when I was nine." His father, Alec, taught classics at Gresham's School in Norfolk, which James attended. " I felt different and in the end rather enjoyed being so. I didn't take drugs. I didn't smoke. I drank a normal amount. I had long hair but I wasn't a hippie. I liked Dylan and preferred the Stones to The Beatles. When I came to London, I discovered the King's Road. It was a very good time to be at the Royal College of Art (RCA), just after David Hockney and Gerald Scarfe had been there."
The young groover's eureka moment came at the RCA. He'd gone to study interior and furniture design but found himself distracted by other subjects. "Buckminster Fuller was hot news, and I became very interested in structures. Fortunately, Anthony Hunt, a very good structural engineer with an interest in design, was lecturing at the college. I went along and was surprised that I - having been keen on art and classics - enjoyed finding out if a beam was going to fail or not.
"Then I met Jeremy Fry, an architect who loved engineering, who had a company that made valve actuators for oil pipelines, but also mass-produced sculptures. This was extraordinary. Here was an engineer as interested in art and design as he was in engineering. Up until that point I believed that people stuck to their professions. Engineers were men in white coats in back rooms, while designers had all the fun in pink shirts designing things with felt-tip pens. Suddenly I was introduced to this world of renaissance men who did both."
A world which he then joined, spending 14 years dreaming up a vacuum cleaner that would replace the "dreadful, wheezing, smelly, noisy, screaming things" that were the only cleaners available to buy when he got married to Deirdre at 28 and started putting a home together. They now live with their three children at the £20m, 50-bedroom stately home Dodington Park in Gloucestershire.
What sustained him through disappointment and frustration? "I just thought it was a good idea. I had no proof that the bag-less vacuum would sell. The fact that no other manufacturer wanted to take it on suggested it wasn't a good idea. But the more rejections I got without any reason being given, the more I was convinced I was right."
He now has the curious reputation of being the man who made vacuum cleaners sexy. The Dyson has appeared on TV, virtually guest-starring in Friends ("Courtney Cox bought one, liked it and talked to the rest of the cast about it, and they thought, 'Wouldn't it be a funny subject for an episode?'") and Will and Grace.
The fashion house Imitation of Christ bought 30 Dysons to be pushed along a catwalk. Dysons have appeared as mannequin accessories in the windows of Barneys, New York. They've even appeared in the "goodie bags" dished out to stars at Oscar ceremonies.
If passports still carried a line defining the bearer's profession, what would Dyson's say? Inventor? Businessman? Designer? Engineer? "It used to be 'Inventor', not because I was showing off, but because it led to funny encounters at customs desks. Lots of people said, 'So you're an inventor? I'm one too, in a small way.'" Dyson laughs. "Now, I'd be happier to be called an engineer. It's what I am. I engineer things. That's where my love is, making things work better."
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