The disgraced Tour de France winner Floyd Landis today made a series of devastating allegations of doping and corruption in the sport of cycling, claiming that former team-mates, including Lance Armstrong, the seven-times Tour winner, used performance-enhancing drugs and that high-ranking officials were complicit in the cover-up of a positive test for the synthetic blood booster erythropoietin (EPO).

Landis, who was stripped of the 2006 Tour de France title after testing positive for illegal amounts of testosterone, also ended four years of denials and protestations of innocence to admit that he used banned substances, including EPO, steroids, human growth hormone, testosterone and blood transfusions, from 2002 onwards. His claims were contained in emails sent to cycling officials and leaked to the media.

Having previously denied the charges against him, even setting up a Floyd Fairness Fund and raising $500,000 (£350,000) to help his defence, Landis said his motivation for speaking out was to "clear my conscience". The timing of his allegations, he added, was due to the World Anti-Doping Agency's statute of limitations; under Wada rules action must be taken within eight years of the alleged offences.

"I don't want to be part of the problem any more," Landis told ESPN. "I don't feel guilty at all about having doped. I did what I did because that's what we [cyclists] did ... Now we've come to the point where the statute of limitations on the things I know is going to run out or start to run out next month. If I don't say something now then it's pointless to ever say it."

Landis, who had three seasons in Armstrong's US Postal Service team, made his allegations in three emails sent to seven cycling officials between 30 April and 6 May. In one of them, sent to US Cycling's president, Stephen Johnson, Landis said he began doping in 2002, the year he joined US Postal, and he then detailed how he was told how to administer blood transfusions, EPO and steroids, without fear of being caught. As well as Armstrong, he implicates team directors, coaches and other top American riders.

Armstrong, who won the Tour de France in each of the three years in which Landis was a team-mate, last night dismissed the claims, questioning Landis's mental state. Speaking before today's stage of the Tour of California, and standing alongside his long-time coach Johan Bruyneel, he said: "We have nothing to hide. We have nothing to run from. If anyone has any questions, we'd be more than happy to answer them."

Asked whether he would sue Landis, Armstrong replied: "Legal action takes time, energy. It takes a lot of money. I have sued a few people in my day."

Armstrong's day did not get any better: he crashed during the stage and was taken to hospital for x-rays.

Pat McQuaid, the president of the International Cycling Union (UCI), reacted angrily, describing the allegations as "scandalous and mischievous". McQuaid said: "These guys coming out now with things like this from the past is only damaging the sport. If they've any love for the sport they wouldn't do it."

The UCI responded tonight to Landis's allegation that the governing body covered up a positive test, saying it "categorically rejects ... the allegation that a positive doping result by Lance Armstrong during the 2002 Tour of Switzerland was concealed after an agreement was reached between the American rider, his directeur sportif Mr Johan Bruyneel and the former UCI president, Mr Hein Verbruggen.

"Deeply shocked by the gravity of this statement, which considerably impinges on the honour of all persons who have dedicated themselves to the fight against doping, the UCI wishes to clearly state that it has never changed or concealed a positive test result." The UCI statement added that Armstrong did not participate in the 2002 Tour of Switzerland.

Wada, meanwhile, promised to investigate. The organisation's president, John Fahey, said: "We are very interested in learning more about this matter and we will liaise with the United States Anti-Doping Agency and any other authorities with appropriate jurisdiction to get to the heart of the issues raised. Wada looks forward to these further investigations and inquiries by those responsible.

"Wada encourages everyone with knowledge of banned practices in sport, including athletes who were caught cheating and who denied the evidence for years, to be forthcoming in disclosing the information they may have to the proper authorities."