"He's going to be a star," observed Prudhomme, to which Stapleton smiled, and responded: "He's a star already."

L'Equipe, the French sports newspaper, agrees. "Lord Cavendish" read the headline on yesterday's front page.

Cavendish's four stage wins doubles the record for British stage wins in a single Tour; single-handedly, he has also ensured that his is the nation topping the table of stage wins. It is the first time that has happened.

In a Tour again beset by doping scandals, with three positives in the first two weeks, Cavendish has supplied not so much a chink of light, but a fireball. Prudhomme, speaking at the start in Nimes yesterday, couldn't have been more effusive in his praise for the young superstar, nor more confident in the veracity of his performances. Speaking before yesterday's 14th stage, the most powerful man in the Tour organisation said: "We can believe in Cavendish, absolutely.

"The thing about Cavendish is he doesn't need (his team to form a] 'train' or to set him up," Prudhomme continued. "He's a pure sprinter. In the final 200 metres he explodes. He's got something extra. He's got that jump. It's pure natural talent. That's not manufactured. It's talent. And it's thrilling."

But where does it come from; and what is it that allows Cavendish to so dominate the bunch sprints? He is not tall, nor physically imposing, nor muscle-bound, as some sprinters are. At 23, he seems still to be carrying a little puppy fat – which is surprising when you consider that last month he finished the three-week Giro d'Italia (winning two stages), and that he is now two weeks into another three-week Tour.

But it seems that as long as his well-drilled Columbia team can do their bit, which is to reel in any breakaways and keep the bunch intact, and then ensure that in the final kilometre Cavendish is up near the head of affairs, then the Manx Express is unbeatable.

His margins of victory have been astonishing, especially on Friday, when he crossed the line a full two bike lengths clear of Robbie McEwen.

In fact, and although Cavendish has been eager to praise his team-mates at every opportunity, they haven't been perfect. Ideally, a sprinter's team will form a train in the final few kilometres – four or five men forming a line at or near the arrow-head of the peloton, with the sprinter sheltered at the back.

Then, one by one, the front man peels off, allowing the sprinter to finally hit the front in the last few hundred metres. That's the plan, anyway, though fatigue seems to have limited Columbia's ability to execute it in the past few days.

The coach who identified Cavendish's talent at a young age, and who runs British Cycling's phenomenally successful academy, of which Cavendish himself is a graduate, says he's not surprised to see his protege emerge as a superstar. Rod Ellingworth recalls that as a junior, and later an amateur, "Mark won by 10 lengths – he played with them. He just had this incredible turn of speed."

Yet Cavendish's physical tests, conducted at British Cycling's headquarters in Manchester, initially suggested that he didn't have the physiology to reach the top. "Physically, he's not very good," says Ellingworth. "His maximum power in tests isn't particularly good, but his style of racing is to conserve energy, sit in the wheels, out the wind, benefiting from everyone around him, so that when it comes to the finish he is fresh and able to unleash that sprint of his. He has to be smart, because he can't rely on his engine – it's not powerful enough."

It could also be that he just isn't very good at tests in laboratories. Like other sprinters, he appears to need bodies around him; people to take on, look in the eye, and then beat. "I always say that sprinters are like boxers," says Ellingworth. "It's the same in athletics. Look at the endurance guys, then look at the sprinters: they have massive egos. That's their character, they're alpha males, with lots of testosterone.

"In a bunch sprint at the end of a stage of the Tour de France there's pushing and shoving; it's a very aggressive environment, you need to be confident. And Mark is very confident."

"All the younger riders have egos," continues Ellingworth, "but I try to get them to use that to their advantage. Mark wasn't always able to keep his in check. As a young lad he used to lose his temper a bit. He was a bit feisty."

Both Ellingworth and the Columbia team director, Allan Peiper, stress that it is Cavendish's confidence and desire to win that sets him apart. "He doesn't want to win," says Ellingworth. "He needs to. If he wasn't he'd pack it in."

"Sprinters need that instinct," says Peiper. "Mark smells the line; he gets more confident as he gets closer to the line. He has complete confidence in his ability. Even last year (Cavendish's first as a professional], he was really struggling, he needed some reassurance, but the confidence was still there.

"There was a stage in the Tour of Catalunya (in May last year] when he was dropped, had to chase all day, but he finished. I was at the Giro but texted him when I heard and said: 'That took the courage of a champion. It's not all about winning, and today you showed you have what it takes to be a champion'."

An intriguing question: who would win in a straight sprint, track sprinter Chris Hoy or road sprinter Cavendish? "Chris every time," says Ellingworth without hesitation. "Chris is a pure sprinter; Mark is an endurance athlete.

"But if you put them head-to-head after five hours on a bike, Cav would walk it."