A tip-off, an anonymous lab and a timebomb under sport

Drugs scandal: The investigation that now threatens Dwain Chambers' career is centred on a pharmacology department in California

The doping scandal that threatens to blow the lid off professional sports and knock some of the top names in athletics out of next year's Athens Olympics began with an anonymous phone call.

The doping scandal that threatens to blow the lid off professional sports and knock some of the top names in athletics out of next year's Athens Olympics began with an anonymous phone call.

A man describing himself as a "high-profile" athletics coach contacted the US Anti-Doping Agency and told it a new designer steroid capable of bypassing standard drug tests had been in wide circulation among competitors at the USA Outdoor Track and Field Championships in Stanford, California.

The caller provided two leads: a syringe purporting to contain the mystery substance, and the name of the man he said had provided it, a well-known San Francisco-area sports nutritionist called Victor Conte whose clients include many of the top names in athletics, baseball and American football.

Four months later, those clues led toraids by federal tax and anti-narcotics investigators, a grand jury investigation focusing on Mr Conte in which as many as 100 top athletes are expected to be subpoenaed, and hundreds of new drug tests based on urine samples taken for the Stanford meeting and the World Athletics Championships in Paris in August.

The naming of Dwain Chambers, Britain's top sprinter, as one of the athletes who initially tested positive for the drug is almost certainly just the beginning. Athletics coaches on both sides of the Atlantic are bracing themselves for a huge scandal.

David Moorcroft, chief executive of UK Athletics, said: "My suspicion is that this isn't about contaminated supplements, it's about the real McCoy cheating." Bill Martin, acting president of the US Olympic Committee, said he did not care how many athletes he lost from Athens next year, likening the purge almost certain to come to "tough love for a high-performing child".

Even Mr Conte, who denies wrongdoing, believes the sporting world is about to witness an upheaval. "As many will soon find out, the world of track and field is a 'very dirty business' and this goes far beyond just the coaches and athletes," he wrote in an e-mail to a San Francisco Chronicle reporter. "Fasten your seatbelts!"

Professor Don Catlin, the world's leading expert on drugs in sport, identified the substance in the syringe as tetrahydro-gestrinone (THG), a synthetic variant of the steroid gestrinone. Professor Catlin, who works for the International Olympic Committee at the University of California at Los Angeles, then developed a test to detect it in athletes. Analysis of top performers began in early August, around the time Chambers was tested at his training base in Saarbrücken.

Meanwhile, the US tax authorities began examining Mr Conte's business, the Bay Area Laboratory Co-operative (Balco), and asking themselves where the financial accounting for THG ­ assuming he had sold it - was recorded. In early September, the tax police, with the Food and Drug Administration, the US Anti-Doping Agency and an anti-narcotics squad, raided Balco's headquarters in Burlingame.

According to unconfirmed press reports, a number of vials and containers filled with anabolic steroids, testosterone and human growth hormone were recovered. The agents also seized computers and documents listing athletes who had their blood and urine tested by Balco as part of the lab's procedure for recommending nutritional supplements.

Those athletes are being ordered to appear before the grand jury - 40 so far, with more expected to follow soon. They include the most celebrated batter in major league baseball, Barry Bonds, whose personal trainer had his house raided after the Balco operation; the US shot-putt champion Kevin Toth, who has also tested positive for THG, and the champion sprinter Kelli White, who tested positive over the summer for the stimulant modanifil.

The first witnesses before the grand jury's closed-door hearing yesterday were Marion Jones, the Olympic 100m champion, and Tim Montgomery, the world 100m record holder.

The athletes are not subject to criminal investigation - and, in the case of the baseball players, not even under threat of disciplinary sanctions because THG is not covered under the list of banned substances in their sport. But they are expected to be questioned closely on their financial relationship with Mr Conte.

Mr Conte has condemned the many leaks from the grand jury investigation and the preliminary dope tests. His lawyers said yesterday: "Victor Conte is presumed to be innocent. That presumption stays with Mr Conte throughout all of these proceedings and is not overcome by speculation and allegations from unknown sources."

Remy Korchemny, Dwain Chambers' trainer, said he sent his athletes to Mr Conte's laboratory because its reputation was "very high quality". He challenged the authorities to prove THG was a performance-enhancing drug, and noted that many modified steroids proved to be useless in practice. He neither confirmed nor denied that his athletes had taken THG, but pointed out that names had been released far sooner than was normal under standard drug-testing procedure. Chambers and the other athletes who tested positive are awaiting the results of second "B" test, after which they can appeal against the findings. Even if found culpable, no athlete is likely to receive formal punishment for several more months.

Graham Shear, Chambers' solicitor, said last night: "My client wants to clarify that he will not accept nor tolerate any accusations or implications that this was a wilful or calculated attempt on his behalf to deceive the authorities. In his eight years in international athletics he has never been tempted to succumb to illegal methods of enhancing a performance." A spokesman for Chambers' club, Belgrave Harriers, said it would be "a tragic development'' in the athlete's career if it was proved he had tested positive for a banned substance. He added: "We are immensely proud to have athletes like Dwain Chambers in our club. However, Belgrave Harriers has never and will never condone the use of performance-enhancing drugs by athletes under any circumstances.''

Mr Conte is a colourful figure in athletics, a former professional bass player who once jammed with Herbie Hancock and was in the group Tower of Power. One band he played for in the 1970s was called Pure Food and Drug Act, a name that bizarrely foreshadowed his current predicament.

He has been in the sports nutrition business for more than 20 years, staking his reputation largely on a zinc magnesium supplement called ZMA, which he says has earned $100m (£60m) around the world in the past four years. Tax authority sources and medical experts cited by the US papers have cast doubt on both the profitability and miracle-working powers of ZMA, suspecting its promotion to be a front for illicit substances such as THG. Mr Conte's lawyers have defended their client's integrity, saying: "Mr Conte is a scientist and businessman who has dedicated his life to helping others, including high-profile athletes."

But he and Balco have been implicated in two other cases. Kelli White was prescribed modanifil by Dr Brian Goldman, a psychiatrist who worked with Mr Conte for 20 years. Balco also supplied iron supplements containing nandrolone taken by the American shot putter C J Hunter - former husband of Marion Jones ­ that led to his ban from the Sydney Olympics.