James Dyson shifts in his seat and laughs awkwardly as his flow of thought hits a tricky obstacle. “God, this is difficult,” he mutters. One of his grandsons called the digital electric motor in Dyson’s new 360 Eye robot vacuum cleaner “the brain” and his own motor whirrs away silently as he analyses the question. Having ranged fluidly for an hour across the history of industrial design, the significance of engineering and Japan’s love of consumer artefacts, he considers the characters of his three children.

Sir James is sitting in his office in Malmesbury, Wiltshire, in the long, wave-profile building that was once its vacuum and washing-machine factory and is now its research and development base. He leans back in his chair, his thatch of white hair and bright trainers standing out against his blue shirt and cardigan. “I suppose all inventors are maniacs, aren’t they?” he ventures. “I was always a bit of a maniac, and very, very focused. Whereas they have a bit more of [his wife Deirdre’s] slightly more relaxed nature, and perhaps they’re more understanding of other people.”

He brightens as he mentions Deirdre, whom he met in 1966, when they were art students. “In many ways, we’re quite similar, my wife and I. We love design. We’re artists, so we design our houses and gardens together and disagree about very little. We went for check-ups and we’ve both got a little node growing on our lungs and a little node growing on our livers, like [symmetrically winged] butterflies. Very different backgrounds but we’ve lived together happily for 46 years.”

James, Jake, Emily and Deirdre on holiday in Holkham, north Norfolk, in 1977

Family life was not always easy. Jake, Dyson’s elder son, remembers his mother teaching art to support them as his father struggled to make his inventions work. “He would be in the cellar day after day, night after night, trying to form a perfect plastic cone [with a machine]. That’s my most vivid memory — of him losing his rag each time it went wrong. But then I also remember when he came upstairs with the perfect one.”

Like his products, Dyson has evolved since he set up his company in a coach house in his garden near Bath in 1993 to launch the DC01 dual cyclone vacuum. But he is still recognisably Dyson: still ambitious, impatient and relentless; still intolerant of mediocrity and the status quo; still his brand’s posh, evangelical salesman; still urging the UK to revive the spirit of Victorian engineers such as Isambard Kingdom Brunel and 20th-century industrial designers such as Alec Issigonis.

I was always a bit of a maniac

“Dyson is a brilliant engineer and an exceptional designer. His love of product sets him apart — he cares about how a product looks, how it performs, how it can be different,” says Anthony Bamford, chairman of the UK construction equipment company JCB. “As an iconoclast, he’ll develop many concepts . . . Those that [work] are wonderful examples of British creativity.”

One of Issigonis’s sketches for the Mini hangs outside Dyson’s office, with the arching lines of the car that embodied the Swinging Sixties, when Dyson was at the Royal College of Art. Issigonis drew it on a balcony of the Negresco Hotel in Nice as he sipped a gin and tonic, a Dyson-like combination of the serious and stylish. “The way [Jake] draws is very similar to the way I draw, which is a good expression of character,” Dyson says of his son. “Powerful drawings with a dark pencil, boldly.”

Some of Dyson’s products have failed — it no longer makes washing machines, for example (“Didn’t charge enough. Learnt that lesson,” he says). Others took a frustratingly long time, including the new robot vacuum, which he first prototyped in 1999 and tried to make work with two variations of technology before devising its self-guiding camera system. Dyson’s machine now lags behind the Roomba, made by his US rival iRobot. It will launch in Japan this autumn and elsewhere later in the year, priced at about £750 in the UK.

Inside Dyson’s product-testing laboratory in Malmesbury, Wiltshire

Yet the company has not only endured but flourished. It has grown from a start-up with four engineers and a few staff answering calls on one phone in 1993 to an operation employing 6,000 in the UK, Singapore and Malaysia, and making pre-tax profits of £240m on turnover of £1.28bn in 2013. Ninety per cent of its sales are now outside the UK. Dyson owns the entire company — which had an equity value of £3.5bn in 2013 and paid dividends of £200m last year — as well as 25,000 acres of land in the UK.

Now, Dyson the company and Dyson the family are at a turning point. Dyson is 67 years old and is not looking back. The diggers have broken ground in Malmesbury on a new £250m “technology campus” that will let him add 3,000 people — many of them engineers — to a UK workforce of 2,500. He is investing £50m in UK universities, including £12m for Imperial College London to start a school of design engineering later this year, and he is putting £250m into expanding operations in Asia.

As it ventures into robotics and software, Dyson faces new competitors — the Roomba is just one example. The “internet of things” — the capacity to link and control devices over networks — is drawing technology companies such as Google, Apple and Samsung into its orbit. Last year, Google paid $3.2bn to acquire Nest, which makes thermostats and fire alarms. That brings both potential — Dyson’s robots could work with others — and challenges.

90% of Dyson’s sales are now outside the UK

So James has called in reinforcements. Having built his own light-making company since 2003, Jake Dyson is folding it into the family business. He became a non-executive board director in 2013, with his brother Sam, a musician and producer, and this cements his place as heir to the Dyson helm. “Jake is highly competent, loves technology, and has good business and marketing sense. He’s got all the things I had and more, because he’s more inventive. So he’ll take it to places I couldn’t,” Dyson says.

As well as a succession plan, it is a declaration of intent — that Dyson will remain independent, not be floated or sold when its founder retires. “The beauty of a family business is that you worry about getting the product right, not about any investors with short-term views or what others think,” Dyson says. “I would hate to be [a public company]. We can be very long term, developing technology that can take years to come to fruition. We can be patient.”

His 42-year-old son has the same faith. “Seeing my father’s work, what he’s achieved, it’s inconceivable to sell that off and watch someone break it into pieces. You know what would happen — they’d pump out 100 products with the brand on, with no engineering improvement, for a quick buck. It’s much more than maintaining the legacy. I’ve got a passion for it and I want to help it grow.”

Sir James Dyson

Age gap aside, it can be hard to tell the difference between James and Jake Dyson. They often dress identically, in clothes designed by Emily Dyson, James’s daughter and Jake’s sister, and her husband Ian Paley; the couple run Couverture and The Garbstore in Notting Hill. “I get all my clothes there and so does Dad. We don’t confer, so we often turn up wearing the same thing,” says Jake, who is wearing a spotted blue shirt.

They also talk in similar ways — launching into long explanations of technology, punctuated with amiable, blue-eyed stares of emphasis when making a point. “I’ll just start from the beginning,” Jake says, when we meet in his workshop and office in Clerkenwell, London, a week later. After 20 minutes, he is just getting into his stride on light-emitting diodes and how they generate intense heat that needs to be cooled in order to stop them deteriorating.

“We soldered it to a copper block with a thin wall at the end, and we clamped the LEDs up against it so the heat shoots out of the back of the LEDs, straight down the heat pipe and is released off the arm of the product. So it becomes an incredibly efficient heatsink, cooled by the convection of air in the room,” he says enthusiastically. “We’re running it at 8.8 watts and we get 560 lumens from it. We chose a warm colour so it’s not the nasty harsh blue that some people use.”

The Dysons are tinkerers by nature. “Jacob used to go into the workshop and start making things on the lathe. I never showed him how to — he’s not very good at being taught,” James says of his son. “Both of us, when we went skiing, refused to have lessons, which is pretty stupid in the case of skiing. For engineering, it’s a good thing because you’re forced to make mistakes and learn from them. You gain this visceral, tactile understanding.”

Jake’s got all the things I had and more

James Dyson was born in Norfolk, the son of a classics teacher at Gresham’s, an independent school in Holt. He went to the school and then, after meeting Deirdre at the Byam Shaw School of Art, studied furniture design at the Royal College of Art. He switched to architecture, where he met the inventor Jeremy Fry. Dyson helped Fry to build the Sea Truck, a glass-fibre landing craft, and his first job was at Fry’s company Rotork. A Sea Truck sits in the Dyson car park, recalling his transformation from designer to engineer.

Like his father, Jake found himself caught by the UK’s education system divide between art and science. At Central Saint Martins in London he became frustrated on his product design course by the emphasis on how things looked, rather than how they worked. “I did a water-powered generator that you’d strap to a drainpipe, so when you flush a toilet, it generates electricity. They were like, what’s that? I went against the grain.”

The easiest way to irk the Dysons is to suggest that their products are successful because of their appearance. Even their supporters say it has been a vital contributor to their success. “To be competitive these days, styling is very important because you can only protect the technology inside with patents for some time,” says Kumar Bhattacharyya, the British industrialist and academic. “Most of the technology in cars is very much the same. When people say it’s stunning, they mean the industrial design.”

‘It’s so exciting, the technologies they’re investing in, the whole mentality of thinking 20 years ahead,’ says Jake Dyson

“Everybody says, ‘These vacuum cleaners sell because of how they look,’ and I say, ‘They sell because they work better,’” James insists. “If something looks designed on the outside but doesn’t work, you hate it and if something’s ugly but works well we come rather to love it. The Aga [oil-burning stove] is an example. Perhaps I shouldn’t slag Aga off, but you know what I mean; it’s not obviously designed.”

Jake made two mistakes earlier in his career. One was to go and work at Dyson in 2000 for a couple of years. Although he found it involving, “I felt like I’d moved back home. I felt that I was in a shoebox. I’d lost my identity and wanted to get out there and prove myself.” That led to a second mistake, which was to stop working for six months while he figured out what he wanted to do next.

“I got very, very depressed and realised that man must work. You’ve got to keep busy or your brain starts dwelling on things that aren’t important.” He rescued himself by renting a workshop in Wandsworth, London where he had a mill and lathe, and would drive there every day from his house in Islington to work on a dual-turbine ceiling fan, which spread wind like a hurricane. (“It lifted skirts 20 feet away.”) He never made it work commercially, although one is fixed to his office ceiling.

Inadvertently, he became apprenticed to a former Rolls-Royce employee called James Campbell Wilson, who owned the workshop next door, in which he tuned suspensions for racing bikes. Wilson would sleep on a shelving rack in his workshop and work mysteriously at night. “I’d leave an engineering drawing there by accident and I’d go in the next day and there would be a gleaming machined part, like the elves and the shoemaker.”

£50m investment in UK universities

There is a lot of his father’s cellar and his late mentor’s workshop in his office. A pair of Pyrex flasks — one filled with bubbling red liquid, the other with cold blue liquid — sit on a table, where he uses them to prove the conductivity of the copper pipes in his lights. His £1,300 Ariel light, intended for offices but also set to appear in high-end furniture stores at the end of the year, hangs above the table.

The building was owned by a lift-engineering company and later became a gallery, which folded when thieves rammed a car through a window to steal a Picasso sketch. There is still a car inside but it is Jake’s — a Fiat 500 that he drives to work and parks in the old loading bay. In the basement there is a 3D printing machine, plus the lathes and milling machines he uses to make prototypes.

His company is tiny compared with his father’s business but it breaks even and he has proved himself to his own satisfaction. “I don’t think I’ll ever feel [trapped] again. I’m well-known in the lighting industry . . . and I’ve achieved everything I wanted to in life. I can say I’ve designed, manufactured and sold five products . . . The journey is so volatile and there are moments of despair, but the feeling when it works is unbelievable.”

His lights will now be sold through Dyson and manufactured in Dyson’s plant in Malaysia. Jake is spending three days a week in Malmesbury, taking part in product development. “It’s growing so fast that if I leave it any longer, it may be difficult to understand the mechanics, get to grips with everything that’s going on there. It’s so exciting, the products they’re working on, the technologies they’re investing in, the whole mentality of thinking 20 years ahead.”

Although James Dyson learnt long ago the value of publicity, he is careful not to let slip what is coming next. Dyson has fought more than 1,200 legal battles over intellectual property, including his first scrap with Hoover in the UK over bagless machines, and is wary of letting any outsiders into his research and development lab in Malmesbury.

I’d treble the engineers if I could

Today, he has conceded. The revolving door turns and we are ushered through, guided at a secure distance from the most sensitive work. We tour through the prototyping area, with 3D printing machines that use 30 tonnes of nylon powder a year to create models. Next comes product testing, with robots pushing vacuum cleaners over patches of dust. Finally, we stand on the edge of a space that was once a production line for washing machines, and is now packed with desks bearing computer screens. The loss of 560 manufacturing jobs when Dyson shifted production to Malaysia in 2002 caused an outcry, but that loss has been more than made up since. Some 1,000 young engineers cram into the space.

They work in a vast hangar-like building, with mauve-painted, undulating beams holding up the roof. There is evidence of its former use — a gantry crane stretches across the roof of the area now used as a canteen. A jet engine stamped Rolls-Royce, one of the early turbojets invented by Frank Whittle, squats in the middle of the canteen. Dyson bought it as a tribute to British technology, like the Harrier jump jet that sits outside the main entrance.

Despite the high security, the laboratory has a playful side. Three plastic colour samples, labelled “Touch Me”, “Look at Me”, and “Smell Me”, as in Alice’s Adventures in Wonderland, hang on a board where we stand. Much ingenuity is invested each year in costumes for the Christmas party. Annmarie Nicolson, a 26-year-old design engineer, built herself wings for the last one and came as Icarus, the son of the master craftsman Daedalus, who, according to Greek myth, flew too close to the sun.

Dyson icons (clockwise from left): 1993 The DC01 Standard upright vacuum cleaner; 2000 The CR01 Contrarotator washing machine; 2013 The Airblade Mk2 hand dryer; 2014 The 360 Eye robot vacuum cleaner; 2015 The AM06 Air Multiplier fan; 2015 Jake Dyson’s Ariel Downlight

Nicolson joined Dyson three years ago, having studied product design in the engineering department of Strathclyde University and spent a year at Mars. She works in New Product Innovation, the early-stage research laboratory at Dyson, and is now in a team of eight trying to create a product that she cannot discuss. If they succeed, it will pass on to the product development division for a year or two before launch.

Dyson spends a lot of time in the laboratory, having handed over day-to-day business oversight to Max Conze, his chief executive. He is chairman and chief engineer, holding monthly “James reviews” to keep his eye on the new initiatives. “It can be nerve-wracking because he’s so inquisitive,” Nicolson says. “He’ll always ask you a question you don’t have an answer to. We’ll sit for hours brainstorming and we’ll filter it down to what we think works best and build a prototype. James will say, ‘Have you thought about this?’ and we’ll say, ‘Well no, we haven’t.’”

Alex Knox joined Dyson in 1993 as one of his first engineers and is now its industrial design director. “James can be impatient, but that’s good. He creates an urgency and a passion,” he says. At the moment, one of the things that makes Dyson most impatient is the UK’s shortage of engineers — his initiative with Imperial is part of his ambition to increase the supply. There were 61,000 UK engineering vacancies last year, and Dyson has to compete to recruit with Rolls-Royce and others.

£250m investment in a new technology campus

Just as lower-cost manufacturing took it overseas in 2002, the ability to hire more skilled workers in Asia is drawing it eastward. “I’d treble the number of engineers here overnight if I could but they don’t exist,” Dyson says. “Part of the solution is to build our engineering resources in Malaysia and Singapore, which we’ve done. We’ve got more engineers there now than we have here. That’s a danger to Britain, because our centre of gravity will shift.”

The biggest danger would be Dyson ceasing to exist or gradually losing its competitiveness. That has happened before to companies founded by British inventors. Jet engines are still made by Rolls-Royce but the Mini was reimagined by BMW, and consumer technology companies that flourished for a while, such as Sinclair, the home computer maker, later faded. Dyson has done remarkably to come this far in a fiercely competitive industry.

Among a pile of gadgets in his office, Dyson has a yellow waterproof Sony Walkman, which he bought in 1985. “I hugely admire them for their technology, design and boldness with new products. A tape recorder that doesn’t record! It takes balls to do that,” he says. But Sony has struggled in recent years. “It is still a wonderful company but I think after [Akio] Morita, they lost direction a bit because he was the engineer,” Dyson reflects.

My father’s not going anywhere

A technology company must be led by an engineer to flourish, he believes. “For me, the revival of Jaguar Land Rover is because [Ratan] Tata owns it and he is a petrolhead. I’ve been to three Grand Prix and he was on the starting grid at all of them,” he says. “An engineer understands the product and the technology. He’s got a pretty good idea of economics, he knows how things are made. He might not know the finer points of marketing or accounting but he’s got the other skills.”

Still, many family enterprises have gone astray when the founder retires because the genius’s children are not geniuses themselves. Jake will face a huge task to carry on his father’s achievements, although he has time to learn — James shows little sign of slowing down. “I’m starting to contribute to designs there and actually saying things in board meetings now,” Jake says. “But my father’s not going anywhere. He’ll be there until he’s 100.”

By that time, who knows what the Dyson brand will represent? As well as education, James has invested some of its profits in farming. He bought 3,000 acres of land in Lincolnshire last year, taking his estate to 25,000 acres — more than the Queen — and has thrown himself into agriculture. “He told me the other day how many peas he’d produced,” Jake says. “He’d worked out the square metres, pods per square metre, and peas per pod.”

Unknown to most shoppers, Dyson’s farms are now filling supermarket shelves. “You go into John Lewis, and you see a range of Dyson vacuums. You go into Waitrose, and the potatoes and the peas have come from our farms. It’s an amazing thing.” But the produce is not stamped “Dyson” is it? “No,” says the founder’s son, lightly. “Not yet.”

John Gapper is associate editor and chief business commentator of the FT. Tanya Powley is the FT’s manufacturing correspondent.

Photographs: Gareth Phillips