British Olympic gold medallist Bradley Wiggins believes the drug-tainted Tour de France has lost all credibility as the race struggles from one crisis to another.

Wiggins and the rest of his Cofidis team were withdrawn from the race after teammate Cristian Moreni failed a test for testosterone. Moreni later admitted to use of the hormone, while being questioned by police.

"No one has faith in who is wearing the yellow jersey," said the 27-year-old Wiggins. "This year's Tour has lost all credibility. It's null and void as far as I am concerned this year. It will take a long time to restore the credibility but I would rather see the hard work put in than give up on it now."

Despite that view, Wiggins dismissed calls for the 2007 race to be cancelled.

"They have to see it through to the finish in Paris," he said.

Some observers have said the spate of doping controversies on this year's Tour have sounded the death-knell for the gruelling race.

In a series of shattering developments, yellow jersey holder Michael Rasmussen was sent home and sacked by his Rabobank team for lying over his whereabouts when he missed a drugs test.

Pre-race favorite Alexander Vinokourov also shamed the Tour through blood doping leading to his Astana team being dropped from the race.

Wiggins admitted that he was so despondent over the crisis that he considered quitting.

"My initial reaction was 'I'm going to get out of the sport'. It was sheer anger but once I settled down a bit, I'm willing to see this thing through," he said here on Friday.

Wiggins insists it is only a minority of riders who are causing the problems.

"The start in London was amazing but things slowly started deteriorating," he said. "Those riders have tarnished the sport and tarnished the Tour de France. It's wrong to say everyone is doing it."