The gypsies have arrived in the playing field opposite James Dyson's Malmesbury HQ. Vast, gleaming motorised caravans are already firmly anchored to the ground, ponies are being trained on leashes, kids are whizzing around on quad bikes - rather up-market travellers, as perhaps befits this stretch of posh north Wilts. 'Hmm,' nods Dyson, gesturing through the venetian blinds that shade the glass walls of his first-floor corner office, 'they came this morning... and the police.'

He seems, for a moment, rather perplexed, as if unused to the outside world intruding, then swivels back to the stone-topped table that doubles as his desk. Charming, urbane, glacially good-looking with his grey hair cropped tight and his pale blue eyes matching the azure of his designer T-shirt, Dyson gives the impression of a man who has long been languidly in control of his own destiny. But gypsies? Here? Then the look of patrician puzzlement turns to a smile.

The field they've occupied, metres from Dyson's futuristic, wavy-roofed factory, was once part of a secondary school, now moved, and could soon be filled with little houses in a private-finance initiative deal. There'll be trouble, he mutters, if the developers turn up now. The site is also - and here's the rub - next to the scrubland where Dyson, Britain's vacuum-cleaner king and one of the most successful entrepreneurs in the country, wanted to build his new factory, expanding production owing to increased demand.

That was a couple of years ago. In the end Dyson never built it, because he decided that north Wiltshire's local worthies would never let him. Another factory? Tsk tsk. So he closed down vacuum-cleaner production here and shifted it to Malaysia, shedding 500 jobs and causing a ruffle of bad publicity at his apparent ruthlessness. Did he care? Seemingly not. Then earlier this year he underlined his insouciance by buying himself a new Gloucestershire home, Dodington Park, one of England's finest Georgian estates, for £15m, as if it would never occur to him that people might make the connection: lay off the locals, hire cheap foreign labour, whack up the profits and buy himself somewhere even bigger to count his millions.

The estate, which he adds to homes in Wiltshire, Chelsea and Provence, is barely 20 miles from Malmesbury, where many of the former Dyson workers live - that, you might think, is rubbing everyone's noses in it. Perhaps the gypsies, like the houses to come, are just here to taunt him. But is he bothered? No. Likewise his reaction to the anger voiced by unions when they heard in March that he was to advise the government on manufacturing in Britain. Him? Of all people?

No. Today, with his mood matching the sun that bleaches the long company car park outside, other people's perceptions are distant clouds beyond his horizon. James Dyson, the man who spent a decade being told his idea for a bagless vacuum cleaner was rubbish and then proved everyone wrong, walks on a different stretch of beach from the rest of us. If there's going to be trouble, who's he to step in?A week earlier, sitting in a small meeting room in London's Design Museum, where he is chairman, Dyson had looked surprised when I asked him why he had based production in Wiltshire in the first place.

'But it's where I live,' he replies, as if to do anything else was nonsensical. In fact, he shopped around before setting up in Malmesbury, almost opening a factory in Wales to take advantage of grants there - only the then Welsh secretary thought his plans for a bagless vacuum cleaner were, well, rubbish. (Step forward, David Hunt - no doubt the valleys are still singing his praises.) That, of course, is the coda to Dyson's early experiences of business-building: being told his ideas were crazy or, worse, stupid.

Design, build and sell your own machines with little outside help in a market dominated by multinationals? He must be mad. No wonder he takes little notice of what others think. And anyway, he doesn't have to. Worth anything up to three-quarters of a billion pounds now, Dyson is still pushing forward. Late last year he launched his vacuum cleaner under his own name in America, a huge market that, if early signals are a good indicator, could double his global sales in the next two years. He now travels monthly to the US, whipping up publicity and glad-handing retailers.

And his innovative Contrarotator washing machine, launched here in 2002 and still made in Wiltshire, is also building revenue, despite constant criticism that it is just too expensive (£699 upwards) to sell widely. Early days, says Dyson, as his vacuum cleaners took at least two years to gain consumer acceptance. He also has a stack of other products waiting to go. As many as 20 are being worked on in conditions of tight security at the research and design unit that stretches half the length of his Malmesbury base. We know one is a robot vacuum cleaner; he even has a prototype on the coffee table in his office. But, being Dyson, he decided his firm had to make its own advances in artificial intelligence before launching it.

Anyone else would have just bought expertise from an outside specialist, but that's not how he works - that's not, he says, how you find true innovation. Then there are the other products he won't talk about, all known internally by code numbers - X21, X22 - not a word whispered to spouses and friends. 'Actually,' laughs Dyson, 'a lot of people here rather like the secrecy.' Most are household products and they will be released, he adds casually, when they are ready. Toasters, kettles, dishwashers, ovens, irons? Garden equipment? He won't say.

So, with all that and toing and froing to America, does he need such a vast new home to fill his free time too? Well, why not? Perhaps, as someone who has achieved success relatively late in his working life, he wants to make his mark. Dodington Park is his statement to posterity: this is me, this is what I have achieved. Or perhaps he just needs to push himself that little bit more. Dyson, public-school-educated, son of a classics teacher, has one of the more complex and contradictory psychological make-ups that you will ever find in an industrialist.

He is, at first glance, a true maverick: a plutocrat who disdains wealth, a manufacturer who cherishes informality, a business-builder who eschews staff share options and jealously guards 100% ownership while nurturing the team ethic in his firm. That, he says, is because he enjoys the risk. 'Almost all entrepreneurs, from Richard Branson back, flog a bit to the stock market so they have a nest egg,' he explains. 'But if my business hits problems, I lose everything; my whole livelihood and wealth is tied up in it. It's terrifying, but actually I quite like it and I think it is good for me. Someone who is safe and secure starts to make the wrong decisions.'

Dyson, says Allan Leighton, the former Asda boss who sits on his board, is a one-off. 'That balance between stubbornness and focus is a fine line.' And it allows him to shape the business his way. 'We are a completely technology-driven company,' says Ross Cameron, formerly of S C Johnson and now head of Dyson's Australian subsidiary. 'James won't release a product unless it is different from what went before. It is the passion for the product that is so different here.'