More than a third of medals at Olympics and World Championships won by athletes who had suspicious drug tests, according to reports.
The allegations surfaced after a whistleblower leaked data from the International Association of Athletics Federations (IAAF) to the Sunday Times and German broadcaster ARD/WDR containing details of more than 12,000 blood tests performed on 5,000 athletes.
Anti-doping experts Robin Parisotto and Michael Ashenden told the newspaper that in their opinion, more than a third of medals, including 55 golds, awarded in endurance events at the Olympics and World Championships between 2001 and 2012 had been won by athletes with suspicious test results.
The newspaper says none of the athletes involved have had their medals stripped from them by the authorities.
The Sunday Times alleges that a top UK athlete is among seven Britons with suspicious blood scores, and 10 medals were won at the London 2012 Olympics by athletes with dubious results.
More than 800 of the 5,000 athletes named in the leaked files recorded blood-test results described as “highly suggestive of doping or at the very least abnormal”, according to the report.
More than a third of the world’s fastest times in endurance events were recorded by athletes whose tests have triggered suspicion.
Mr Parisotto said: “Never have I seen such an alarmingly abnormal set of blood values.
“So many athletes appear to have doped with impunity, and it is damning that the IAAF appears to have idly sat by and let this happen.”
Mr Ashenden said: “For the IAAF to have harvested millions of dollars from the broadcasting of athletics events around the world…yet only devote a relative pittance of those funds towards anti-doping, when they could see the terrible truth of what lay beneath the surface, is… a shameful betrayal of their primary duty to police their sport and to protect clean athletes.”
The Sunday Times reported that the IAAF had threatened to take out an injunction preventing the newspaper from publishing details of the files before dropping the legal action on Friday.
IAAF vice president Sergey Bubka said it was too early for an official statement from the organisation.
But he told reporters: “In every case, we must be precise and correct. We must follow our rules, our regulations. The IAAF position – it’s my personal position always – zero tolerance for doping, we must protect the clean athletes.
“What should we do and how we will act for the future, the improved regulations, I am always very, very firm for this position, personally. For that, in this situation now we must follow and it will be responded by IAAF.”
WADA president Sir Craig Reedie said: “WADA is very disturbed by these new allegations that have been raised; which will, once again, shake the foundation of clean athletes worldwide.
“These allegations require swift and close scrutiny to determine whether there have in fact been breaches under the World Anti-Doping Code and, if so, what actions are required to be taken by WADA and/or other bodies.
Five-time Olympic rowing champion Sir Steve Redgrave said: “There have always been cheats, there have always been those who have sought an advantage.
“The powers that be in sport, in this instance the World Anti-Doping Agency (WADA), need to be one step ahead of this rather than one step behind, as they have been at times.”
British Olympic heptathlon champion Jessica Ennis-Hill – who lost out on gold at the 2011 World Championships to Russian athlete Tatyana Chernova, later given a two-year doping ban, said: “Like so many other clean athletes I put my faith in the system operated by the IAAF and WADA and focus on training.
“I very much hope both organisations can respond to the latest allegations quickly so athletes and fans alike can carry on with confidence believing that progress is being made in tackling doping in our sport.”
British middle-distance runner Andrew Baddeley, who was beaten by suspect runners during a major event, said: “In an awful way, nothing surprises me any more.
“Doping now seems to be so widespread that it’s difficult to prove you are clean.
“Look at what happened to Chris Froome in the Tour de France . He was being accused of cheating when there wasn’t a shred of evidence to support it.
“The IAAF need better funding and better resources to tackle this problem or else nothing is going to change.”