"I been on TV and awards bashes and dinners and Downing Streets and Buckingham Palaces. I've met the Queen, I've met her sons. She was OK. Blair, Thatcher, Major, Brown. I've done it. there is no fun in it. None. Whatsoever. It is boring."

What an anticlimax it must be to win The Apprentice, I reflect, waiting in the cramped, sub-zero lobby of Amstrad HQ. Imagine bashing through those boardroom double doors in triumph, to find yourself in charmless, cheerless Brentwood, in a nondescript Seventies office block, rather more David Brent than Donald Trump. Perhaps the show is just too lavishly art-directed, because the contrast between the whip-smart, plate-glass, go-faster 24/7 business world it projects and this sleepy, provincial uncoolness is somewhat comic.

If you call Amstrad after 5.30pm you reach an answering machine. Sir Alan Sugar’s own modest, grey boardroom looks out not over some dynamic cityscape but an industrial estate receding into Essex scrubland. His real PA is not the pretty popsy who tells quaking candidates, “Sir Alan will see you now,” but a nice, motherly woman called Frances. And Sir Alan himself has forsaken a sharp business suit for slacks, slip-on shoes and a woolly, blue waistcoat.

But then refusing to care about appearances, distrusting flashy modern fripperies is true to Sir Alan’s no bullshitters, schmoozers or arse-lickers, what-you-see-is-what-you-get business mantra. And he certainly doesn’t pretend to be anything except a bored and grumpy 60-year-old man who is barely tolerating a bunch of idiot questions while trying to remember not to swear.

When he smiles it is mirthless and appears manufactured, as if to say “Look, I’m being nice, what more do you want?” He is impervious to jokes, gossip or mild teasing. This is certainly not an interview where I would normally proffer a personal anecdote. But despairing at his flat answers, I blurt out that my ten-year-old son has started a business selling his home-made marmalade, and suddenly Sugar comes to life. “Excellent!” he exclaims. “A man after my own heart! He made the marmalade at home, obviously?” I have the sticky cupboards to prove it. “You should charge him gas and electricity, that will throw a wobbly on him.” He chuckles thoughtfully. “Very good, very enterprising.”

Later, explaining how Gordon Brown – “he regards me as a role model” – sends him on speaking tours to encourage young people into business, he returns to my budding marmalade magnate. “If Brown heard about your son it would be manna from heaven. If he thought that young people at the age of ten are already beginning to think that way… Because most kids of ten just want to know where their next pair of Nike trainers is coming from or their iPod. But no one is going to give you any presents when you’re a bit older. And the earlier you learn to fend for yourself the better it is.”

And then he’s off about his Hackney council estate childhood, the fourth child of a poor family, third-generation Jewish immigrants from Eastern Europe. His first enterprise, aged 11, was photographing kids and selling the snaps to their grandparents. He made and flogged ginger beer, cleaned cars, sold repackaged black-and-white film and by the time he left school was earning more than his father, Nathan, a tailor, and knew a life of noble wage slavery would not suit him.

His first proper company sold car aerials to vehicle accessories shops. By 21, he had founded Amstrad (a conflation of Alan Michael Sugar Trading); by 33, he had floated his company on the London stockmarket, and at its apex Amstrad was worth £1.2 billion. Now it is valued at around £130 million, although Sugar’s personal wealth – mostly from his property empire – is around £780 million.

Entrepreneurs, he says, are born, not made: business skills can be acquired just as any fool can learn the piano. But the ability to see an opportunity, the alchemy of turning that into profit, is a God-given talent as surely as perfect pitch. “I don’t come to work like my dad, to support my family. The days of doing it for the money are long gone. I come to work because I’m also looking to do a bit o’ business, a better deal. It’s something in you, something you never lose.”

And indeed, talking about any other subject Sugar is bored and boring. Business is the game, the buzz. Yet the question hanging over his career is how such a consummate entrepreneur, the man who first put a personal computer in the average home, has not ended up running the biggest corporation in the world?

“You’re right. You’re exactly right,” says Sugar ruefully. “But I’m a trader by nature. I’m a trader. And a trader cuts things back when things aren’t going well, rather than investing all the money in to going forward a bit further. I’m a trader, and I’ll never change from that. You look back with hindsight and we could have been a much bigger business. But [he claps his hands decisively] I’m happy with what we’ve got.”

In 1988, Amstrad’s new PC2000 developed hard-drive problems and had to be withdrawn, damaging the firm’s reputation. So Sugar moved away from computers towards the embryonic satellite TV market. Today the vast majority of Amstrad’s business is making set-top boxes for BSkyB (in which News Corporation, parent company of The Times, has a 39.1 per cent stake). In February delays in delivering new high-definition versions sent Amstrad’s half-year pre-tax profits plummeting by 16 per cent. City analysts say that Amstrad is vulnerable: it would be in trouble if Sky decided to buy its boxes elsewhere.

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