SIR ALAN SUGAR is in a good mood. “I love this, I really do,” he says, wrinkling his bristly face. He is pointing at two Amstrad e-mail phones sitting side-by-side on the wide desk in front of him.

“Every analyst and fund manager says what a f***-up I’ve made with these phones. Well, just to pour oil on the fire, we are going to bring out another one later this year, and I am going to shove it right up their arses when they realise they have got it so wrong.”

His dark eyes glint maniacally. Sugar, boss of Amstrad, abrasive, pugnacious, a man who, in his own words, dishes it out with the “John Blunt” approach to management, is indulging in his favourite pastime — “having a shout”. Sitting behind a clutch of screens and keyboards in his sixth-floor office at Brentwood, Essex, he just can’t stop.

“And what you don’t understand is that these same analysts and fund managers stood by and watched Vodafone piss £20 trillion billion up the wall in subsidy, infrastructure and all that stuff, and it’s fine. They say, ‘can you go out and lose another £50 billion please?’ It’s okay for them to subsidise phones and stick bloody great antennae where everyone doesn’t want them and lose money, it’s great, because they’re subscriber-building — well, that’s what we’re doing, innit?” I had only asked him how his e-mailers — home phones with little screens for e-mailing and net browsing — were selling, and off he goes, biff, bosh, very nicely thank you, 300,000 out there, 16 grand a day profit on the service, up yours. Next topic, please.

What I had really wanted to know is whether, as rumour suggests, he is about to buy Pace, the television set-top box maker that strode into Amstrad’s market half a decade ago and is now on its knees. On this, however, he is uncharacteristically reticent.

But surely he doesn’t need the brand — because punters don’t care where set-top boxes come from — and he already has the same technology? Also, if he wanted the Pace people, he could just poach them. What’s to buy? Contracts? Off the record, he teases, “I am not telling you anything. Ha!” Then he orders me to read a piece he wrote about Pace in these very pages six years ago, which rather presciently lays out what was likely to happen to the once-lauded firm.

Sugar, 55, one of the country’s best-known entrepreneurs, loves to be proved right. He has been ranting since the 1980s about the City, about electronics, about football — just about anything he has got involved with, really. Some find his growling aggression frightening but that’s to misunderstand the fun he has playing up to the caricature.

Sir Stanley Kalms, former Dixons boss and an old sparring partner, calls Sugar “the straight-faced comedian”, always willing to have a pop but often only for a wind-up. You just don’t want to bump into him on a bad-mood day. Then he can really tear your head off. But the next day it will be all cheery, how’s ya doin’? That’s Sugar’s style, not letting anyone in too close, keeping everyone guessing. Trim, neat, as impeccably suit-and-tied as he is roughly spoken, he is rarely comfortable in teams. Ask him how he plays his favourite sport, tennis, and he replies “from the baseline, aggressively, singles”.

Sugar has always been a loner. Son of a Hackney tailor, third-generation Russian Jewish stock, he was born a good 12 years after his three siblings and got used to playing cowboys on his own. His early working life proved his mettle: still in his teens, he chucked in a civil-service job doing statistics to become a salesman flogging electronics. Then he realised all his boss was doing was importing and selling on. He could do that himself, and Alan Michael Sugar Trading — Amstrad — was born. Three decades on, he has a £600m personal fortune built on his head for figures, talent for spotting a deal and disciplined approach to work. He is nicer than he pretends, too. Behind the gruff persona, he gives generously to charity and accepts government invitations to lecture and advise.

But ask if he could have created something even bigger, a truly global business behind Amstrad word processors or hi-fi equipment, and he is sanguine. People say he missed out because he can’t delegate. “The limit of Alan’s powers are in the scope of his personal control,” says one rival. “Yeah, fair comment,” shrugs Sugar.

Any move to boost his electronics interests aggressively would be a shift in gear right now. Recently he has run Amstrad, which sells consumer electronics, and privately owned Viglen, which supplies computers to the public sector, without pushing either as hard as he could. Instead, he has shifted profits into property. That’s his safety net: something for his three grown-up kids. “I do all my gambling in electronics but on the other side of my business, I gotta be safe.”

Companies like Amsprop now own chunks of London’s West End, skewing his wealth far more towards bricks than chips, and bringing his singular talent for negotiation-by-abuse to a fresh marketplace.

“Property agents?” he wrinkles up again. “Tossers. They are all total tossers. Don’t know what they are talking about.”