The 32-year-old's appeal to be allowed to swim in Sydney was turned down by the British Olympic Association yesterday.
Fibbens, Britain's fastest 100-meter freestyler, tested positive for cocaine at a meet in Sheffield, England, in 1998 and was banned for two years. His suspension was later reduced to a year because FINA, swimming's world governing body, acknowledged that he had taken the drug for recreational purposes.
Under the rules of the BOA, anyone who fails a drug test is automatically barred from ever representing Britain in the Olympics.
Fibbens had appealed on the ground that the offense was minor but, for the first time in its history, the BOA's independent panel on doping threw out the appeal, stating that the offense was not minor. It ended Fibbens's hopes of becoming the first swimmer in British history to compete in four separate Olympiads.
"I am saddened that such an experienced and seasoned Olympic athlete as Mike Fibbens has found these standards too high to uphold and regret that he will not be in a position to join Team GB in Sydney," said Simon Clegg, the BOA's chief executive.
This year the BOA cleared the hockey player Russell Garcia to compete in Sydney even though he too was guilty of an offense involving cocaine. But in Garcia's case the BOA cited a clause in the International Olympic Committee's medical code which states that cocaine is not covered by sanctions in out-of-competition testing.
British Swimming Federation Chief Executive David Sparkes said he felt Fibbens had been harshly treated by the BOA.
"I understand the position they [the BOA] have taken but there does seem to be an element of double jeopardy," he said. "Effectively they are retrying the case."
More successful yesterday were the sprinter Doug Turner and the hurdler Matt Douglas, who were cleared to compete for Britain in Sydney after they won appeals after drug-test failures. Their bans were lifted because only the stimulant ephedrine was involved.
"Ephedrine is a common ingredient in many cold remedies and readily available across the counter throughout the country," Clegg said. "The IOC treats a first-time finding for ephedrine as its most minor doping offense and it would have been entirely inappropriate for the BOA to impose a lifetime ban for this offense."