Until now, Jones denied doping, even suing BALCO founder Victor Conte in 2004 for $25 million. Conte repeatedly accused Jones of using performance-enhancing drugs and said he watched her inject herself. “It cost me a lot of money to defend myself,” Conte said yesterday. “But I told the truth then, and I’m telling it now.”

In her letter, Jones said she didn’t realise she’d used performance-enhancing drugs until she stopped training with Graham at the end of 2002. She said she lied when federal agents questioned her in 2003, panicking when they presented her with a sample of “the clear,” which she recognised as the substance Graham had given her.

Jones’ career has been tarnished for years by doping allegations against her. In August 2006, a urine sample tested positive for EPO, but she was cleared when a second sample tested negative. She was also among the athletes who testified before a BALCO grand jury in 2003. Her former boyfriend, Tim Montgomerie, also testified, and was given a two-year ban for doping in late 2005.

USA Track & Field was not aware of Jones’ letter nor any pending legal action, CEO Craig Masback said. “Anything that exposes the truth about drug use in sport is good for ensuring the integrity of sport,” Masback said.

Darryl Seibel, spokesman for the US Olympic Committee, declined to comment on whether Jones would lose her medals until legal proceedings are completed.

The Washington Post also reported that, in her letter, Jones said she lied about a $25,000 check given to her by Montgomerie, who pleaded guilty in New York in April as part of a criminal scheme to cash millions of dollars worth of stolen or forged checks. He is yet to be sentenced.