Sprinter Mark Lewis-Francis, who ran the anchor leg in a shock 4x100 metres gold at the Athens Olympics, has tested positive for cannabis but will be allowed to continue competing.
The 22-year-old failed a dope test after winning a silver medal in the men's 60 metres at the European indoor championships in Madrid in March.
UK Athletics said on Friday Lewis-Francis would lose the medal but no ban had been imposed.
"UK Athletics hereby issues Mark Lewis-Francis with a public warning for a finding of cannabis in a sample which was collected from him on March 5, 2005 in Madrid, Spain," a statement said.
"UK Athletics confirms that the athlete is disqualified from that competition. No period of ineligibility has been imposed and the athlete is free to compete."
Doping rules allow public warnings if it is the athlete's first anti-doping rule violation and where there was no intention to enhance performance.
"UK Athletics and the (world governing body) IAAF are satisfied that these factors all applied in Mark Lewis-Francis case," the statement added.
In one of the upsets of last year's Games, Britain pipped the United States to relay gold, with Lewis-Francis holding off 2000 Olympic 100 metres champion Maurice Greene in a blistering last leg. It was Britain's first gold in the event for 92 years.
Lewis-Francis was a replacement in Athens for Dwain Chambers, banned for two years for testing positive for the designer steroid THG (tetrahydrogestrinone).