Bradley Wiggins, the British Olympic champion, has hit out at the "pure stupidity" of the doping scandals that have threatened the race and forced his own exit from the competition.

Wiggins has been withdrawn from the event after his Cofidis team-mate, Christian Moreni, tested positive and was questioned by police following the end of yesterday's stage.

Wiggins, a fierce anti-doping advocate, said: "It is completely gutting to have to quit the Tour, but everyone knows where I stand on doping. It's pure stupidity on the part of Moreni. I don't know how he can have slipped through the net.

"That is the way it goes. It's just unfortunate. When you get a team of 26 riders there may always be one idiot."

Wiggins, 27, also admitted that the continuing controversy over the Tour - race leader Michael Rasmussen on Wednesday followed Moreni and Cofidis out of the event when he was sacked by Rabobank for "lying about his whereabouts" in training -made him reconsider his career.

"It makes you think about your future as a professional cyclist. You say to yourself, what is the point? I could be doing better things'.

"But then you think why not continue because I get a lot of pleasure out of it. Why should I give up because of one individual."

David Millar spoke out again yesterday after the latest doping scandal to rock the event. The Scot, who served a two-year ban for doping, said: "He was playing the system and had to go. It shows that teams are reacting rather than putting their heads in the sand. Finally, team management and sponsors are accepting responsibility, which they weren't before.

"I think it's a great day for cycling and we're definitely moving in the right direction, but we can't stop here. There's a long way to go."

Pat McQuaid, the president of the International Cycling Union, believes there is hope for a drug-free competition, perhaps as early as next year. But he called on riders and teams to take their share of responsibility for staying clean.

"The teams need to control the riders, they're the ones who need to clean out the ones who are iffy, they need to guarantee the riders are clean and riding fairly." But at the end of the day, the riders take the decision to put something in their bodies. The rider is the one who makes the decisions."