The head of UCI, world cycling's governing body, says that positive drugs tests show that the sport is taking its anti-doping mandate seriously.

UCI president Pat McQuaid admitted that it would be unrealistic to suggest that doping would be eradicated from the Tour.

But he added that the single positive test on the 2011 Tour, which found Katusha rider Aleksandr Kolobnev had been using the masking agent hydrochlorothiazide, suggests that the Tour is successfully catching cheats.

"I don't think it's ever possible, not just in cycling but in any sport, that you're going to get no cheaters," he told the Associated Press.

"It's not a bad thing, it shows that the system's working, it shows that you're catching people, and it shows that if a rider does take a product that is an illegal product that it can be caught and found in the system."

And McQuaid added that if nobody had been caught doping on this year's Tour, "you'd probably say there must be something going wrong here."

The UCI is carrying out doping tests on the Tour participants on a daily basis, and the regime has attracted complaints from some riders about its intensity.

Two days after his now infamous crash through a barbed wire fence, Vacansoleil's Johnny Hoogerland revealed to ITV that he had been woken up at dawn by drug testers to provide a urine sample.

However, the UCI has also granted last year's Tour winner, Alberto Contador, permission to ride in this year's race, despite the threat of an arbitration hearing next month which could yet find him guilty of a doping offence.