World cycling chief Pat McQuaid has launched a broadside at the handling of a doping investigation which has left the UCI virtually unable to sanction riders suspected of cheating.

A police investigation in Spain last May, dubbed Operación Puerto, allegedly uncovered a drug and blood doping network being run by a Madrid-based sports doctor, Eufemiano Fuentes, which implicated 58 professional riders, some of them top names in the peloton.

Yet three months after an apparently explosive scandal, cycling's world ruling body may well be forced to allow most of those implicated to return to racing following a Spanish judge's ruling that evidence from the investigation cannot be used to obtain sanctions.

The results of the UCI’s effort to study hundreds of pages of evidence in a bid to obtain sanctions against the likes of Ivan Basso and Jan Ullrich - who were suspended from the Tour de France by their teams because of their alleged involvement - appear to be on hold for the time being. UCI president McQuaid, told AFP Saturday that of the 58 riders involved "12 to 14 are seriously implicated in Operación Puerto."

McQuaid said at least another dozen were under "some" suspicion while the rest of the 58 were implicated only because their names appeared in documents or telephone conversations, which had been tapped by investigating police.

McQuaid feels he has been let down by the authorities in Spain.

But as the sport has huge anti-doping reforms which are gaining widespread support, the Irishman is sure he will be supported by teams and sponsors alike in this instance at least by demanding that suspected riders provide DNA samples to clear their names.

"The Italians have closed the files on Basso, and he has been cleared to race. The Spanish have also closed files on riders who have been involved," McQuaid told AFP. "To be fair to the Spanish authorities, they were proactive in trying to carry on the investigation and they contested the judge's decision.

"I am more disappointed with the Italian authorities," he added, "but I blame very much the Spanish on this. The Spanish police uncovered a doping network whose sole objective was to help get riders out of the sport who were cheating, but despite all the evidence pointing to this it has all been shelved by the Spanish judge.

"It's a ridiculous situation,” McQuaid said. “Our hands are tied at this point."

Giro d’Italia winner Basso, who has always denied involvement, was cleared this week to race again by the Italian cycling federation after two Italian Olympic Committee (CONI) hearings ruled that there was not enough evidence to sanction the former CSC rider.

Basso, along with Ullrich and Francisco Mancebo, had been suspended prior to the Tour de France after evidence from Operación Puertolinked them to the affair. Since being released by his team, Basso has been talking to other teams including Discovery Channel. However the 29-year-old is not yet able to sign for a ProTour team. A major stipulation of the Pro Tour's code of ethics is that riders involved or suspected of being involved in doping affairs are theoretically barred from joining other Pro Tour teams.

McQuaid conceded that there may be riders implicated in the affair who are perfectly innocent. In an effort to clear the cloud of suspicion, McQuaid has proposed a solution to end the suspicion by demanding those implicated to provide DNA samples, so they can be compared to the results from the 200 bags of human blood seized in raids on apartments leased and owned by Fuentes.

"A lot of riders may have gone through trials by media," McQuaid said, "but the message from the teams' representative body (AIGCP) is clear. They want riders who have been implicated to provide DNA samples. It's a reasonable solution. They don't want to welcome back riders who may have a cloud of suspicion hanging over them.”

While Ullrich is reported to have supplied a DNA sample to clear his name, Basso has so far refused.