JOHN CAUDWELL comes with a reputation: self-made, hard-driven, uncompromisingly aggressive. An alpha male among entrepreneurs — ex-model girlfriend on his arm, helicopter parked round the back of his Jacobean mansion — the Stoke-based, bullet-headed tycoon has built up an £840m personal fortune by being harder and sharper than just about anyone else in the mobile-phone market.

Through his Phones4U retail chain and other related businesses he shifts phones faster than his competitors, certainly in more volume than anyone else, with hard-sell techniques and an employment record that often seem only inches away from controversy. And he does not apologise for that.

“Our business is a business for winners,” he says in his flat-vowelled Potteries brogue. “Motivation is by carrot and stick. That doesn’t mean I beat people up, by the way . . .”

But he doesn’t mind encouraging the misconception, either. And it’s not an act. Unions moan about conditions in his workplaces. Colleagues admit he’s intimidating. Rivals say he’s insecure. All agree he can be very tough to do business with. One who has dealt with him describes him by such a rude word I don’t think I can even asterisk it. Television viewers got a taste of it last year watching him harangue potential new recruits in an episode of BBC2’s Trouble at the Top.

But where was the trouble? Reviewers may have been appalled by Caudwell’s behaviour but the man himself says he was just making a point. “Working for me is tough, it’s not for everybody, and I wanted the programme to show that. But for people who want to be a winner and have ambition, there’s no finer place to be than in the Caudwell Group.”

Certainly it has furnished him with the trappings of achievement. He is sitting on a luxurious white sofa in his pin-neat Chelsea flat overlooking the Thames as he speaks. Dressed in cords and an expensive checked shirt, he seems more at ease than his reputation would allow. Tall, lean, athletic in build, his balding ginger hair cropped short and his face a mass of pale freckles, he looks younger than his 50 years — the result of a punishing exercise regimen — and when he narrows his eyes, only slightly menacing.

Nor can you quibble with his sales success. Turnover at his private group of companies, which includes the retail chain Phones4U, hit £1.4 billion in 2001. Figures for 2002, according to Caudwell, will show a leap to £2 billion. But something else is bubbling up, too. For the past month there have been rumours that he might be selling part of the empire — Singlepoint, an airtime reseller — to Vodafone. He also wants, it seems, to soften that hard-nut image he has worked so diligently to cultivate in the past.

On Saturday he is opening his Staffordshire mansion and estate to host a vast charity ball, one of the biggest in Britain, in aid of the Caudwell Charitable Trust, which donates to the NSPCC and others. Hmmm. This is the man who last year was making headlines for paying himself in gold bars and platinum sponge in order to minimise National Insurance (NI) contributions. So what’s being polished now? “Hogwash,” he says sharply, anticipating my drift. Then he smiles. “Actually, it’s an understandable thesis to put forward, that I’m buffing up my image, but it’s still hogwash. I was doing charity work even before I got bad press, and I’m certainly not using charity work to counter it.”

Caudwell, like many bruiser-bosses, enjoys a bit of verbal sparring. Those who work closely with him say he may “dish it out” on a regular basis, but he respects those who stand up to him, and that beneath the confrontational manner, there is a more sensitive heart beating. He is a loyal friend, a devoted father, a man who looks after his own — he just puts all that to one side in the workplace.

At the office he has the classic entrepreneur’s mistrust of outsiders and a single-minded belief that he has to keep on top of everyone who works for him all the time. Now he has 7,000-plus employees, that must be a strain. It is, he smiles. He is learning to be more “macro” now.

So is he selling Singlepoint? He shrugs and starts a deliberately tortuous response. “If I were to answer that question you would form one conclusion, but in answering that over a period . . . ” OK enough, yes or no? He won’t say. “But I’ll tell you this: if there is any truth in these stories, which aren’t being leaked by me, then the publicised price of between £200m and £400m is not a price I would sell for.”

Sounds like he is already in negotiations. Others in the telecoms sector contend that he must, at some stage, want to cash in what he has built, if only because much of his wealth is notional, vested in the paper value of the firms he has created.

He shakes his head. How many times does he have to say it? He wants to build his business, not shrink it. And his lifestyle is well supported already. Since 1998 Caudwell Group has paid £11m into an employee-benefit trust, “to assist in the recruitment and motivation of key staff”, for the potential benefit of Caudwell and his dependants. The money is under the control of independent trustees, but gives him an income of some £2m a year. Why should he flog businesses now? Then he adds: “Of course, if at any time in the future the shareholder value of a business was jeopardised . . . ” The main shareholder being him? “Yeah.” Then he’d flog it sharpish? He laughs loudly.