The entrepreneur and innovator tells Simon Garfield about inspiration, determination and why he doesn't do email…

Thirty years ago this month, Clive Sinclair launched a computer that he hoped would change the world. In the majority of cases it only changed the way people played primitive computer games, but it also turned a bespectacled, prematurely balding man into a hero for our times.

In those dark days before Windows 7 and the iPad, the Sinclair ZX80 represented the pinnacle of affordable domestic computing. It was a flat box without a screen or proper keyboard, it had the memory of a hamster and at the back of it was something that looked like a radiator grille but was actually a strip of plastic designed to look like a radiator grille. It promised it could do "quite literally anything, from playing chess to running a power station", which was good value for something costing £79.95 in kit form and £99.95 assembled, about one fifth of the price of other home computers.

Sir Clive, who was knighted for services to industry at the age of 43, will be 70 later this year. He lives in an apartment overlooking Trafalgar Square, and from his adjacent office he has a magnificent view of tourists and lions (recently he also had a view of people performing on Antony Gormley's fourth plinth, but that "got a bit boring really"). He was a household name before Sir Alan Sugar, and for a while was the unlikely future of modern electronics: a bright, hi-tech uncle rejuvenating British industry blighted by decay, unions and Thatcher.

Sinclair helped transform Cambridge into the computing capital of the world, a homegrown version of Silicon Valley and Taipei, and for a couple of brilliant years he made the bestselling computers in the world. And then the competition took him on, and his great machines went the way of the Spinning Jenny, and here he is in his carpet slippers nursing a heavy cold.

He says his recollections may be a little blurry, but he is clear on one thing. Before his other inventions made him poor, the ZX80 and its successor the ZX81 made him rich. "Oh my lord, yes," he says as he settles on a sofa. "Oh good God, yes. Very much so. I'm just speaking from memory here, but within two or three years we made £14m profit in a year. That would be a lot today."

He says that the ZX80 computer was named after the year it appeared, and because the letters sounded cool and futuristic. He is keen to credit the rest of his small team at Cambridge, not least Nine Tiles, the company that made the Basic operating software. But he is a little hazier about what the machine could actually do.

"We had several routines you could be doing within minutes," he says. "People could tap in a few keys and make the display do some strange things. All very exploratory. We had a little printer, and one guy, right at the start, came out with the program that generated hypothetical dinosaurs. It invented their names, and printed out their pictures, and it could go on doing this indefinitely. Then very soon a huge number of games came out and the whole thing exploded."

"Not literally?"

"No."

The ZX80 sold about 50,000 units, and the ZX81 which replaced it cost £69.95 and sold 250,000. The brochure promised that a child of 12 would soon be mastering "decimals, logs and trig", although the trig would have to be saved to a cassette recorder. The average 2GB laptop of today has 2,000,000 times more memory than that offered by Sinclair's first machines, although he is keen to stress that computing ability isn't everything. "Our machines were lean and efficient," he says. "The sad thing is that today's computers totally abuse their memory – totally wasteful, you have to wait for the damn things to boot up, just appalling designs. Absolute mess! So dreadful it's heartbreaking."

Sinclair, who is not an especially tall man, has always been a great one for the smallness of things. He made those little pocket calculators, he made black digital watches, and also those pocket televisions on which the newsreader Kenneth Kendall looked like Angela Rippon. Later he would make the little C5 (1985), way ahead of the game in the quest for an electric car, so long as you didn't actually try to take it on the road.

He says the important thing about his computers was not only their ability to help with domestic chores (when WH Smith sold them it stressed you could "flummox your bank manager"), but also their capacity to expand the user's intellectual horizons. But it was the male hobbyists who had the most fun: adverts depict fathers programming train timetables with their sons while mum brought in the Victoria sponge.

Things really took off when the ZX became the Spectrum in 1982, and colour games such as Jet Set Willy became the second major activity in teenage bedrooms. Like the Chopper bike, these amusements are now retrospectively popular again, although Sinclair sees none of the rewards. When did other companies such as Atari and Commodore begin to catch up? "I don't think they did catch up. We never had any serious competition in the sense of making machines that were cost effective by comparison. The BBC machine Acorn was quite expensive, and only succeeded because the BBC put its name to it, which was quite outrageous. Then the IBM machine took over. Not because it was a good machine – it was a completely appalling design, but it was IBM, so you know…"

And what computer does he now use himself?

"I don't use a computer at all. The company does."

"So you don't do email?"

"No. I've got people to do it for me."

"If friends and family want to communicate?"

"They can do that. We've got a computer in the front office, but I get someone to do it for me."

"That seems odd to me. Why is that?"

"Sheer laziness I think. I can't be bothered."

"Do you not know how to operate it?"

"I do know how to, but I don't."

"Sorry to press, but it seems the simplest thing in the world to do your own emails."

"Well I find them annoying. I'd much prefer someone would telephone me if they want to communicate. No, it's not sheer laziness – I just don't want to be distracted by the whole process. Nightmare."

When he's not not doing his emails, Sinclair occasionally appears in the tabloids pictured with a blonde former lapdancer 36 years his junior ("He's actually incredibly attractive to women," his intended, Angie Bowness, whom Sinclair met in Stringfellows, has said.). The rest of the time he continues in his attempt to reinvent the wheel. He walks across the corridor to his office, where one section is given over to the A-Bike, his miniature lightweight folding bicycle. He launched this in 2006, and it costs £199.99. He says it's selling well, and that he's just solved some manufacturing problems. I pull one out to sit on it.

"They're not necessarily working models," he says, "so I'd rather you didn't."

I ask him how it folds up. "I won't go into that now if you don't mind – I'm not feeling too well."

I ask him what else he is working on.

"A little electric car."

"And what can you tell me about that?"

"Not much."

"When might it be viewable?"

"I hope within a year."

"Any resemblance to previous efforts?"

"No, it doesn't look like anything we've done before."

"But obviously all the big companies are doing their own electric cars."

"But they won't be doing what I'm doing, I'm sure. As usual I hope I'll sell lots of them. But who can tell?"