Surely Sir Alan Sugar's Mr Angry turn on The Apprentice is an act. In reality, as with many celebrities, he will be different from his primetime persona, searing Apprentice contestants over a high heat, then eliminating one after a firestorm of baleful invective with a finger jab and “You're fired”.

Crisp in dark suit and white shirt, he is not exactly effusive when we meet at the production company that makes the show: a reedy “hello”, no shake of the hand.

If you are a fan of The Apprentice, tonight's first episode of the fourth season is fantastic: two teams of men and women, prettier and more toxically self-aggrandising than any previous year's, try to sell some fresh fish with butt-clenchingly embarrassing results. Early villains emerge; the boardroom scenes are painful.

“They're not a bad-looking bunch, which makes for comfort viewing,” the bearded Amstrad founder admits. He sees the players when they come into the “boardroom” for the first time, telling them unnecessarily that he's “no Mary Poppins”.

Yes, he says, some are there only to be famous (remember Katie Hopkins from series three?) “but they'll never get the job. That becomes apparent in the way they want to be in front of the camera. But more importantly” - his Cockney bruiser accent rises menacingly - “they are useless at business, and that's why they exit the process.”

The room is cold, he seems colder. Are you as rude as you appear on screen, I ask the side of his head (he doesn't look at me for much of the interview). “What you see on screen is me, there's no question of that,” Sir Alan says. “But it is the side of me the BBC chooses to show. There is more light-hearted banter, which hits the cutting-room floor because it doesn't put bums on seats. It's a one-way portrayal, not the whole of me.”

The Sugar story is well worn: he grew up in working-class Hackney, sold vegetables to greengrocers, then sold car radio aerials and electrical goods, and set up his first company at 21. Home computing and electricals made him very rich. He was a controversy-courting chairman of Tottenham Hotspur. His company, Amstrad, was sold last year to BSkyB for £125million. With his interests now focused on construction, property and aviation, his personal wealth is valued at around £800million. The Apprentice has made him a rather more upscale Simon Cowell.

If he's not Mr Angry, who is he? “You've got to be able to laugh at yourself, at disaster, in the business world. It keeps you sane. I'm sarcastic when things go wrong, that's what you don't see. But it's right to show me angry...” The voice rises again. “This isn't Dancing On Ice or Strictly Come Dancing. It's business boot camp.” So we shan't expect cameras inside the Apprentice mansion following romances? He looks horrified. “This isn't Love Boat. Even if it was happening we wouldn't show it. We're not about that.”

Is any of it staged? “No way does the producer tell me what to do or say. None of it is orchestrated, acted or scripted. Any decision made in that boardroom is mine. There's no, ‘Keep this one, get rid of that one'. I wouldn't put up with it. That's how I am in my business. What comes out of me is natural. I didn't go to acting school.”

Sir Alan is glumly fixated on The Apprentice being about business. “It was a concern from the very beginning that it doesn't become panto - not while I'm involved in it,” he says grandly. “It's about the real thrust of business. I am a champion of enterprise. The show has a great following among young people, it highlights basic errors and why you get the simple thing done before you move to something more sophisticated. The younger generation of business person has this fast-track-to-success aspiration, to leapfrog to getting an airline like Richard Branson, forgetting all the drudge work he did.”

He disagrees that viewers feast on the show's rows and tension. “I am who I am, and I suppose that's what the BBC sees in me,” he says, although without his “eyes and ears” - Margaret Mountford and Nick Hewer, who follow the candidates and report back to him - “there would be no show”, he adds generously.

“Siralan” (the two words now roll together) hopes he chooses the right winner every year, although “clearly not in the second series”, when Michelle Dewberry won. She left Amstrad after only a few months. “The girl had potential but her aspirations were different from mine,” Sir Alan says.

He says that he admits when he's wrong. “You don't listen carefully enough to me saying ‘Sorry, you're right' [presumably the “you” means journalists]. You only focus on me bollocking people.” I am about to say that the programme's producers, rather than journalists, focus on that, when he adds: “You're never shown that.”

Just what is eating him? He seems to hear slights where none have been levelled. It occurs to me that if you said “Good morning” to him, he would probably retort, “Good morning for who?”

But Sir Alan is genial, nostalgic even, talking about his childhood in Hackney. “I always felt I'd have my own business. I've always been a salesman. I never wanted to be a rocket scientist or a football player. One of the things that drove me to be self-sufficient was looking at the way my father [a tailor] struggled to keep the family going. I thought, ‘I don't want that'. He did a very good job of bringing up a family of four children in very tough times.”

Sir Alan was the youngest, the nearest of his siblings was 12 years older, “so I was a bit of an only child. We lived in the council blocks and we did all the good things. You could play in the streets, playgrounds, build bikes and carts. You can't roam around in these terrible times we live in now.”

At school he was good at science and maths. He left at 16. University was “never on the radar, we couldn't afford it, you had to start providing income to the home”.

His first job was working as a civil servant at the Ministry of Education. How was that? Uh-oh, the finger jabbing starts up: “It bores me talking about it again and again.” Did he want to be an entrepreneur? “You don't ‘want' to be an entrepreneur. People call you an entrepreneur in recognition of what you've done. I was a salesman - wheeling and dealing and trading.”

Did he want to be as rich as he became? “No. All I was interested in was being self-sufficient and providing for my family [wife Sue and their three children]. I became a wealthy man relatively early. My wife and I took to wealth easily. We come from similar backgrounds; money has never changed our personas. I've still got friends I had when I was 15 - taxi drivers, salesmen. I am who I am (he says this a lot). I have that businessman's instinct of wanting to make money; that's my job.” To what end? “Nothing. No end.” He laughs scornfully. “End?! Until they put me in a wooden box, I suppose.”

Has the Sugar empire felt the effects of the credit crunch and market downturn? “No. Because of my wealth of experience one has gone through the valleys and mountains of these things before. The one we're in at the moment will bottom out and we'll rise again. I've tailored my business to be immune from doom and gloom by not overstepping the mark, by cutting our cloth according to what we can afford. You have to sit on the fence in periods of depression and be ready to pounce when the time is right. We're not indebted up to the neck. We own property in prime locations. If we go through a two or three-year period of remaining stagnant, so be it.”

Sir Alan is one of a group of business chiefs who advise Gordon Brown on enterprise, and is proud to be “the rough diamond, the streetwise member of the mob”. Is he down on academic qualifications? “The winner of last year's Apprentice [Simon Ambrose] got a 2:1 from Cambridge. Does that answer your question?” Not really. “They [qualifications] are meaningless in the world of business. They are a badge that shows a person is at a certain level of intelligence - it doesn't demonstrate that they are an expert in anything. The learning starts when you come into industry.”

Controversy has long bubbled around his attitude to women: does he think women are good for the workforce? “Absolutely,” he says. Does he have an issue with childcare? “It's not an issue for me,” he says angrily, and decries quotes “taken out context” and extrapolated into headlines - “I don't know if you've got the balls to write that. I doubt you will.”

“I have great sympathy for women,” he says. “I think some of the employment laws are counter-productive. They prevent employers asking questions, which 99 per cent of the women would be happy to answer.” What questions? “Where they live, whether they have children, have they made provision to have their children looked after. It gets blown out of proportion by the media. In a similar way, you've been questioning me [he is suddenly angry again] about the way I'm seen on The Apprentice as being rough and gruff, and that's because it suits the BBC and it suits you people to write that side of it because you twist the story.”

You're being pretty rough and gruff right now, I say.

“Yeah, it's annoying; you're another one who's fallen for the trap.”

What trap? I simply asked if you were as rough and gruff as you appear on television - and as you're thumping your hand on the table, it would seem that you are.

“If you're not happy with the interview you can terminate it now,” he says. There's more grizzling [him] and incomprehension at the sudden outbreak of said grizzling [me]. “Well, you're not there when I make the original comments [on TV],” he says. “And you like to edit them in a way that sells newspapers.”

Deep breaths. What if he asked a woman about childcare and she hadn't made provision for it? “Well, you'd hope that the woman would think ‘It's a good point he's making'. Here's an exclusive clip for your article,” Sir Alan sneers. “Be under no illusion. There are women employers who are more ruthless than men. Women employers think about the point more than men do. They are more conscious of not employing other women because they feel they're not going to get the value of work out of them. I think it's right for women to be asked the question and I think it's right for women to volunteer the information ... companies have no divine duty to help with childcare. Companies employ people. It's the Government's responsibility to provide childcare. You pay a person a salary and they cut their cloth accordingly.”

Given Sir Alan's rock-hard self-belief, it is perhaps surprising that he admits to having doubts. “Always. Doubting whether you've made the right decision, whether the products are right, whether you've invested too much, paid too much, sold too cheap - constant doubts.” How does he resolve them? He finally looks at me, albeit with an expression of derision. “You don't resolve them. They resolve themselves. The proof of the pudding is in the outcome of the scenario.”

What have his best of times been? “Anything,” he says, far from sunnily. “There have never been any bad bad times. Bad times is when you lose a family member, lose a friend, when you're very ill or one of the family is ill. Nothing else is bad. Bad is when you hear of people being killed, disasters, terrorism, murdering and stabbing - that's bad, right? Nothing else is bad. This is only money. Money's nothing. How much you've got of it is nothing. It means nothing. You had a happy childhood with nothing and I've got a happy life with something but who cares? It doesn't bother me at all.”

Sir Alan relaxes by watching TV, reading magazines, “playing on the old computer” and flying planes. He has homes in Spain and Florida “but this is my country and I like being here the majority of the time”. Was turning 60 significant last year (he turned 61 on Monday)? Gosh, he smiles. “Yeah, every ten years is a milestone. It's psychological, isn't it? When you turned 20, you thought someone who was 60 was half dead; one foot in the grave. In myself I feel much wiser, cleverer. I keep fit.”

Does he have any further ambitions? “In business you never know what's around the corner, that's the exciting thing.” Some people think about their mortality...

“I'm not some people,” he growls. “Did I not say ten minutes ago that I'll stop doing what I do in my grave? I'll do what I want to make me happy. If I want to start planting tulips, I'll do that. Or daffodils. Or cloning different types of roses.”

Sir Alan will stop making The Apprentice “the day I don't enjoy doing it”. It should stay an annual event, rather than the American version, featuring Donald Trump, which he thinks has “thrashed the concept to death by running three seasons back to back ... the public are always the ones who have told me the right thing to do with my products. If the public don't tune in to The Apprentice any more, there's a polite message there.”

I wonder if it will be like the “polite message” he sends by leaving without even a cursory farewell. But, as Sir Alan is so fond of saying, “I am what I am”, and he clearly feels that, in the words of the Gloria Gaynor song, he “needs no excuses”.

The Apprentice, BBC One, tonight, 9pm

The Apprentice: Winners so far

Series 1

Tim Campbell, 30:

the Eastender

A psychology graduate from a poor background, Tim was working for London Underground when he applied. After a successful stint with Amstrad, he left to form a male grooming business and set up a trust to help young entrepreneurs.

Series 2

Michelle Dewberry, 28:

the dropout

Having worked her way up from the KwikSave checkouts, Michelle was already a high earner as a self-employed telecoms project manager. She made headlines for revelations about the accidental death of her sister, and abuse at the hands of her father. She quit four months into her job at Amstrad, after losing a baby by a fellow contestant and difficulties with Sir Alan. She now runs her own consultancy firm.

Series 3

Simon Ambrose, 27:

the rich kid

Public school and Cambridge-educated Simon had already worked at an investment bank and run his own internet shopping channel when he went on the show, which he narrowly won. He is now working for Sir Alan and training as a surveyor.

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