The Tour de France was nearing a fitting climax here yesterday, with rumours of further doping scandals and drug-based revelations spreading through the convoy like wildfire. If the latest speculation is proved correct, tomorrow afternoon’s traditional finish on the Champs Elysées will be a wake, rather than a celebration.

Sandy Casar, riding for the Française des Jeux team, eased the home nation’s pain with a stage win in Angoulême, but his hard-won success barely distracted from the real business at hand: debating the viability of the Tour itself.

In Manchester yesterday, Bradley Wiggins, having spent most of Wednesday evening in the company of the French gendarmerie after Cristian Moreni, who tested positive for elevated levels of testosterone, and the rest of his Cofidis teammates had been excluded from the Tour, was outspoken in his criticism of this year’s race.

“No one has faith in who is wearing the yellow jersey,” the 27-year-old Briton said. “This year’s Tour has lost all credibility. It’s null and void as far as I am concerned. I’ve had no regrets that I’m not still there. It’s not a nice place to be.”

Wiggins had spent most of the build-up to the Tour start in London reiterating his belief in drug-free sport. “My initial reaction was, ‘I’m going to get out of the sport,’ ” he said yesterday. “It was sheer anger, but now I have settled down a bit, I’m willing to see this thing through.”

Wiggins insisted that cycling’s culture of doping, first laid bare during the 1998 Tour’s “Festina Affair”, was being driven out of the sport. “Five riders have tarnished the sport and tarnished the Tour de France,” he said. “A minority are willing to push the boundaries. Older guys that were back there in 1998 are still willing to see how far they can go without being caught.”

However, Wiggins maintained that there were riders in the peloton whose ethics could be trusted. “It’s wrong to say everyone is doing it,” he said. “It has made me determined to come through this and prove that there can be clean winners in this sport.”

The International Cycling Union (UCI), the sport’s governing body, was under intense pressure yesterday to justify its doping programmes and its apparent unwillingness to invoke an article in its own regulations, which states that any rider receiving a warning over his failure to comply with antidoping regulations within 45 days of the start of a Tour could be prevented from competing.

Pat McQuaid, the UCI president, maintained that he was “absolutely committed” to drug-free sport, despite a bitter response by the UCI to calls from Dick Pound, the World Anti-Doping Agency (Wada) president, for a world summit on drugs in cycling.

“Wada is now criticising the UCI for having found banned substances, which is the consequence of any effective antidoping campaign, and is preparing to stage a show trial instigated by its president, Richard Pound, who during the Tour de France has constantly made condescending comments about cycling,” a UCI statement read. “The UCI refuses to be subject to a farce.” The denouement of the race is likely to turn on this afternoon’s individual time-trial, from Cognac to Angoulême. Alberto Contador, the leader since Michael Rasmussen was evicted from the race, will battle to hold off Cadel Evans, of Australia, over the largely flat 55-kilometre route.

Based on past results, Evans may well usurp the Spaniard, although in this volatile Tour, few would be foolhardy enough to predict the final outcome.