Drugs in Sport: It started as a rumour, seemingly from nowhere, as these things usually do. It was the Sunday lunchtime of the IAAF's World Athletics final on September 14th in Monte Carlo. The American hurdler Chris Phillips had just been revealed to have tested positive at the World Championships in Paris the previous month for the banned drug modanafil.

That was the same stimulant for which Chambers's training partner Kelli White had tested positive and will ultimately lead to her being stripped of the gold medals she won in the 100 and 200 metres in Paris.

Now groups of journalists huddled together to discuss the latest report that Chambers was caught up in the affair. But when questioned, officials from the IAAF were bemused. They were adamant that no more cases were outstanding from the World Championships and they certainly had no information that Chambers had tested positive for any banned substance. The rumour withered on the vine.

Then two weeks ago it reared up again. A training group in the north of England had heard that Chambers, the European 100 metres record holder and champion, had failed a drugs test. The tip-off came, the athlete assured a reporter, from someone who would know. But still calls to the IAAF and UK Athletics drew no information.

The IAAF were insistent that they did not understand why they kept receiving calls from Britain asking about Chambers testing positive for banned drugs.

Last Friday the plot began to thicken when the chief executive of the United States Anti-Doping Agency, Terry Madden, told reporters during a telephone conference call that they had discovered a new designer anabolic steroid called tetrahydrogestrinone (THG). Madden revealed its production had been traced to Bay Area Laboratory Co-Operative, Balco, whose founder Victor Conte was Chambers' nutritionist.

Mark Brodie, a spokesman for Stellar, said it would be dangerous to make a link between Chambers and Conte and that newspapers should be careful before they published the information. This was despite the fact that earlier in the year Conte had contacted the Guardian on Chambers's behalf after he had been linked with Dennis Mitchell, a convicted drugs cheat who had been hired by Stellar as a coach.

What Brodie did not know was that Chambers and his training partners had been targeted by the IAAF for an out-of-competition drugs test on August 1st while they were training in Saarbrucken, Germany, under the coach Remi Korchemny, following a tip-off from the US Anti-Doping Agency.

The discovery of THG was so sensitive that only a handful of officials knew that it even existed and were determined that the information would not leak out. The samples were flown back to the International Olympic Committee-accredited laboratory at the University of California in Los Angeles where Dr Don Catlin had covertly established a test for the drug.

There was, however, a delay because of the sheer volume of samples Catlin had to test. But when he got round to analysing Chambers's urine sample, it showed traces of THG.

The IAAF were informed and on September 30th officials called UK Athletics to break the news. Chambers was contacted a few days later and told of the adverse finding. But even then Chambers continued to act as if he had done nothing wrong. On Tuesday he turned up at Crystal Palace as part of a school sports mentoring programme and happily coached a group of young children.

Meanwhile his agent John Regis, the former European 200 metres champion, met with a blunt denial calls to Stellar's offices asking whether Chambers was involved in the THG scandal.

But while Chambers was signing autographs in south London, a source close to the case revealed details of his positive test to the Guardian.

When Brodie was contacted at 6.47 p.m. on Tuesday he said that he would need to contact Chambers. He then rang back six minutes later and threatened legal action if the story ran. By then it was too late. Chambers was already fighting to save his career.