“I was in this Toyota dealer at the weekend looking at a car,” says Peter Jones, “and the woman behind the desk screamed ‘Omigod. Omigod. It’s Peter Jones from Dragons’ Den. I can’t believe it.’”

Jones, 38, boss of Phones International, looks bashfully proud. The success of Dragons’ Den, BBC TV’s pinstripe version of Pop Idol, has caught him by surprise, but like any good entrepreneur he is quick to see the opportunities.

No downsides to television fame? He widens his watchful eyes. “I can’t think of one, actually. Nobody’s come up to me yet and said, ‘you’re a complete tosser’.”

The PhD-wielding engineer who was laughed off last week’s show might have been tempted. Jones’s acerbic verdict on the engineer’s idea for a wooden-clad computer — “You say you’re a doctor? I think you need one” — could become one of the business put-downs of the year.

Jones makes a face when I bring it up. Feeling guilty? A bit, he says. It’s partly in the programme’s editing, which winnows out the politeness and leaves the acid, but also because, in the end, he does believe it’s best to be blunt.

Or maybe because the Dragons’ Den entrepreneurs — tech investor Doug Richard, Yo Sushi chief Simon Woodroffe, Red Letter Days founder Rachel Elnaugh, fitness-centre boss Duncan Bannatyne, and Jones — have a role model to live up to? “Yeah, I guess everyone’s typecast me as the Simon Cowell of business,” says Jones, quick to grasp the mantle.

Is that a good thing? “Well, Cowell speaks his mind and so do I. If I see someone in front of me and the idea is ludicrous, I am not going to hold back.”

Even if it’s needlessly hurtful? “It is dismissive,” he nods, “but I think we have saved a lot of people from losing their shirts. It’s like saying, wake up, get real, smell the coffee.”

I only ask because, in the flesh, Jones seems rather different from his television persona. Sitting in the Institute of Directors, jacket off, his 6ft 7in body crouched over a tiny meeting table, he exudes boyish charm. With his flopping hair and eager-to-please smile, you might take him for many things — plausible salesman, ageing sportsman — but tough-nut boss is not one of them.

Yet Jones is by far the most successful of the “dragons”, with a Buckinghamshire business that sells and distributes mobile communication products and has grown from nothing in 1998 to a turnover of £150m. He also has an estate in Surrey, two houses abroad, a fleet of sports cars and says he has wealth outside Phones International of “in excess of £100m”. His company adds another £150m to £200m “without question” , he reckons. It makes you wonder why he quibbles over the odd £50,000 on the show.

That’s probably because, behind the charm, he is sharper than most about money. Ask John Caudwell, the Phones 4U founder who has a reputation for being pretty sharp himself. Jones ran logistics for Caudwell for a year, then walked out to set up Phones International as a direct rival. Ouch.

A falling-out? No, just chalk and cheese, according to Jones, who says he prefers a more consensus-driven style. (Caudwell, away skiing, declined to return my call, but others say the tension between the two is still palpable.) And, before that, he worked in computers for Siemens Nixdorf, had his own bar and restaurant, ran a software start-up that went bust, set up a tennis-coaching firm at 17 — he played to county standard but preferred money-making to glory on court — and never went to university. In other words, for all his youthful appearance, Jones has packed more work into his two decades in business than most manage in a lifetime.