Clive on high

He deserves his reputation as a pure genius - and also as a bit of a prat. But in his new King's Cross penthouse, Sir Clive Sinclair is lord of all he surveys. By Rosie Millard

I'm not suggesting a loft conversion above King's Cross Station is the same as Sir Norman Foster's 1,265ft-high monolith, planned for the City of London, but both Sir Clive Sinclair's new penthouse pad, designed for one person, and Sir Norman's tower, designed for two banks and a hotel, are, in their way, on the same grand millennial scale.

"It is rather wonderful," says Sir Clive, with slightly more than a touch of the understatement. We are padding about on his open-air terrace one hundred feet above King's Cross Station. Below us, the station's double arches are in a constant state of admitting and expelling dozens of brightly lit trains; behind it looms the single dark vault of St Pancras. Over to the left is the winking pyramid top of Canary Wharf; far behind the myriad spires of Wren is the Palace of Westminster. Behind us rears the black mound of Highgate Hill.

Although the penthouse itself is all elegance and minimalism, its location is not exactly salubrious. Indeed, it backs onto one of Britain's most notorious red-light areas on one side, and onto one of its largest rave clubs on the other. "I like the communications around here,'' says Clive, when asked to comment on the suitability of his new neighbourhood. A somewhat unconventional answer, that, but then Sir Clive is a hardly a conventional bloke.

Probably the country's best-known inventor, he was knighted in 1983 and yet does not quite fit in with the established image of a scientist. He's celebrated as a genius, and is chairman of Mensa. Divorced from his wife of 22 years, by whom he has three grown-up children, he is also well known for stepping out with a succession of young glamour-pusses. "The boffin, the blondes and the curious chemistry of sexual desire" read one tabloid headline last year. His tremendous technological advances - the first pocket calculator, the first populist personal computer (the Spectrum) in 1979, digital watches - suddenly made electronics available to most people in this country. Yet his popularity did not save him from derision when some of his inventions, such as the C5 electric car in 1985, didn't quite catch on. None of these contradictions seem to grab him at all. In fact, Clive is much keener on solving problems like individual flight or bicycles that will fold up like an umbrella.

Back downstairs, we are quaffing gin and tonic in the spectacular glass and steel observatory that he calls a sitting-room. "I heard about loft conversions five years ago, and I've been searching for one ever since," he says. Previously, he was living in somewhat cramped conditions in a Mayfair flat. His life was on hold and his furniture in storage, due to rather complicated antics with various women and to the sale of his vast family houses in Chelsea and Cambridge.

And then he chanced upon Battlebridge Basin, an area next door to King's Cross Station. Battlebridge Basin, legend has it, was christened to honour a tremendous fight between Boudicca and the 14th and 20th Roman Legions (she lost and is supposedly buried underneath what is now Platform 10). Currently a rather seedy area of kebab shops and car-washes around the Grand Union Canal, it also boasts York Central, a tall white warehouse which advertises itself as having "The Largest Loft Conversions in London". Clive bought the top two floors; David Bailey has since snapped up the one below.

From the personal lift entrance onwards (you know you've arrived somewhere in life when you have a lift entrance of your own), it's clear that Clive is as fond of this new habitat as any (or all) of his inventions. York Central has been, at various times, a sacking factory, a wedding-dress manufacturer and a storage place for Royal British Legion poppies. When Clive bought his share in it from developers London Buildings, it was derelict. Since then, architects Harper McKay moved in and built him a three-bedroomed apartment that houses his office, two kitchens, two bathrooms, a study and the glass-walled sitting-room. The cost? "I will only say it was somewhere in the region of pounds 750,000," he admits meekly. Some of his less successful inventions may have cost him dear, but he is clearly still a very rich man.

There are three things to remember about Clive Sinclair. First, he doesn't really give a damn. "Do I wish I was like Bill Gates [of Microsoft-and- richest-man-in-the- world fame]? Absolutely not at all." Second, he's an enthusiast. He still has his name and number in Directory Enquiries, and DIY inventors are always using it. They ring Clive up with their own inventions, and he is rather sweet to them down the phone. And third, he's not interested in looking back, not awfully. There's a glass cabinet in his new office with a few of his inventions scattered in it (prototype digital watches, calculators, the Spectrum, that sort of thing). They may have changed the way we live, but their inventor is not overly concerned as to whether you notice them, or not.

He's certainly not mad about discussing his high-profile chairmanship of Mensa. One suspects that Clive has, at long last, got rather fed up with Mensa (possibly due to Press fascination with those famous weekends for members where the intercourse does not just involve the cerebellum). At any rate, he's decided to throw in the towel and, after 16 years at the top, he's stepping down.

His company is currently immersed in the Zeta lightweight bicycle battery, which he's trying to develop for wheelchair users. But apart from this, his interests are, for the moment, focused on his immediate habitat. He designed all the interiors of the apartment in York Central, from the pale blue floorboards, to the ingenious fluorescent floor-lighting track (which bounces light up to and off the white ceilings), and came up with the minimalist blue / white decor which runs throughout, even down to the duck-egg and cream marble chess-set on the kitchen worktop, at which point witness a classic Clive conversation.

RM: "This chess set is lovely, Clive."

Clive: "Yes, it is rather."

RM: (slightly overawed) "I suppose you must be brilliant at chess. Do you play against computers?"

Clive: "No, actually, I don't play at all. I can play, but I don't. I just bought it because it matches the colour scheme."

Once such honesty is established, Clive's apartment becomes rather good fun. There's the Bang and Olufsen hi-fi in the kitchen sideboard, which slides open and glows at you when you wave your hand at it. There's a spectacular 1978 Steinway grand, which was owned by Clive's grandfather. ("I don't play, actually, but please play yourself if you'd like to." I do, it's dreamy); there are also some nice big modern paintings, sculpture and a little gas fire next to a comfy sofa where you can sample his large collection of poetry (an art form he clearly is at home with).

It's enough to make living in King's Cross seem quite inviting, another of Clive's concerns. He's already hosted lunch meetings with the local councillors, a youth leader and P&O, who own much of the land around Battlebridge Basin; he's concerned with giving opportunities to people in his new borough of Islington. "Do you know what the unemployment rate here is for young people? It's 40 per cent! That's what Tony Blair should be concerned with. He lives just up the road, for God's sake."

What Clive really fancied before he got into loft conversions was a Scottish castle. "I just couldn't find one. I wanted one which was really in the country. But the castles I found were all actually on farm land, so you would just step out from the castle straight into a farm. Not ideal when I wanted to step out into a real wilderness." What he's ended up with, of course, is the exact opposite. Throughout the apartment, the ingenious floor lighting cuts down internal reflection; the huge curtain-less windows are full of the constant light and movement from the city which surrounds them. "Sometimes I wake up at three in the morning, like one does. I've been doing rather a lot of that lately. I go outside, out onto the terrace. All the lights of the city are still on. I wait until dawn comes up over Docklands, and it's amazing." Rather than hover above London on his penthouse floor, Clive Sinclair is immersed in it.