Justin Gatlin’s coach claimed that athletes are able to get away with doping because the drugs they use cannot be detected by tests.

Explaining the nature of “designer” synthetic drugs, Dennis Mitchell, a former 4x100m world record-holder who in 1998 was banned for having high testosterone levels, told The Telegraph’s undercover reporters: “There’s a lot of different things going on out there.

"There’s the simple easy stuff, and then it goes all the way up to very complex things.

“The complex things are safe in terms of getting tested because they can’t find it. The simple things, those are the things you’re gonna get busted on.”

Mitchell’s remarks recalled the Balco doping scandal that ended the track  career of Robert Wagner’s wife Kelli White, and brought the British sprinter Dwain Chambers’s cheating to light.

Experts are increasingly concerned by the emergence of tailored steroids that are not only almost impossible to detect, but evolving so fast as to leave anti-doping authorities playing an endless game of cat-and-mouse. Yet the precise extent to which performance-enhancing designer drugs are being used in sport is unknown.

Man-made versions of naturally occurring chemicals such as testosterone are “tweaked” to retain their effects, while staying ahead of testing regimes.

Designer steroids made headlines in 2003 as part of one of the largest-ever doping scandals, the Bay Area Laboratory Cooperative (Balco) affair.

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Trevor Graham, the coach of the Americans Tim Montgomery, Marion Jones (then the fastest man and woman in the world) and Justin Gatlin, sent a syringe containing traces of a previously unknown substance to the US Anti-Doping Agency (Usada).

San Francisco-based Balco was already the subject of a federal investigation into allegations the company and its owner, Victor Conte, had been supplying athletes with banned substances since 1988.

Using Graham’s sample, the International Association of Athletics Federations (IAAF) tested 550 athletes for the designer steroid tetrahydrogestrinone (THG), 20 of whom registered positive.

Conte, coach Remi Korchemny and two others were charged with conspiring to “distribute performance-enhancing drugs” to dozens of professional athletes in 2004. They were eventually convicted of handing out a testosterone-based masking agent referred to as “The Cream”, and an anabolic steroid, “The Clear”.

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Dennis Mitchell gave evidence to the FBI, while Gatlin was reported to have secretly recorded more than 10 telephone calls with Graham as part of the investigation.

Among the high-profile athletes banned for taking drugs supplied by Balco were Montgomery and Jones, while Jones was jailed for lying to the FBI in 2008. 

Chambers, who was coached by Korchemny, was banned from the Olympics for life and stripped of his post-2002 titles, but returned to competition in 2005.

The full investigation