Dwain Chambers has been suspended pending a disciplinary hearing after his B sample tested positive for banned steroid THG.
The 25-year-old faces a suspension of up to two years which could deny him the chance to compete in the Athens Olympics next year.
Under British Olympic Association rules he would also be banned from all subsequent Olympics.
Chambers’ B sample was tested at a laboratory in Los Angeles on Monday and a statement on Friday from UK Athletics read: "The B sample analysis has been conducted and confirms the finding in the A sample.
“Dwain Chambers has now been suspended by the IAAF pending the result of a hearing before an independent Disciplinary Committee.”
Chambers has protested his innocence, his legal advisors stressing on Friday that contrary to earlier reports, there has never been an admission by their client that he took THG or any other banned substance.
The athlete has also claimed he was categorically assured that the only supplements he had been given were those which complied with IAAF anti-doping rules.
Chambers, who is the European 100m champion, first tested positive at a training camp in Germany on 1 August.
UK Athletics chief David Moorcroft revealed that Chambers has until 8 December to request a hearing.
He added that he was still uncertain of what happens next regarding the silver medal won by the 4x100m relay team at the World Championships in Paris.
Chambers was part of the team and any competitions or prizes won after the positive test become null and void if an athlete is found guilty of a drugs offence at their hearing.
“What we don’t know is whether the IAAF would intend to take the medal away during the suspension period or suspend judgement on the medal pending the outcome of the hearing,” said Moorcroft.
‘Inconclusive’
In a statement, Chambers’ lawyer Graham Shear said: “I believe the results of the B test do not provide any conclusion to this matter whatsoever.”
He added: “This is just the beginning of a lengthy process. Until satisfactory explanations and answers for these questions can be provided, nobody is in a position to make judgement on Dwain Chambers’ alleged culpability.”
John Regis, a director of Stellar Athletics Club which manages Chambers, released a statement supporting his client and calling for a system of accreditation for coaches, nutritionists and supplement manufacturers to be set up.
The statement said: “It is increasingly evident that athletes have to unconditionally rely on the guidance and expertise of those advising them and whilst there are no moral or ethical standard codes of practice or a monitoring governing body for those whom they rely upon, they remain largely unprotected while entirely responsible.”