Froome leads the way at Mont Ventoux but questions about doping prove harder to outrun

Froome had dealt with the matter calmly during his first week in the maillot jaune even as Team Sky's patience began to wear thin; Sir Dave Brailsford, the team principal, having appealed to reporters for ideas as to what he could do to answer questions conclusively. He even invited the World Anti-Doping Agency to come and give their verdict on whether Froome's results are credible.

It was a cynical comment but one which will likely have felt cathartic since yesterday's discomfiting press conference had come just hours after Froome produced a scintillating display on Ventoux to extend his overall lead on the Tour.

"I just think it's quite sad that we're sitting here the day after the biggest victory of my life, a historic win, talking about doping," said the Sky rider. "My team-mates and I have been away from home for months training together and working our arses off to get here, and here I am accused of being a cheat and a liar."

Froome has become the focus of the sort of speculation which now tends to be attached to anyone who takes the lead in the Tour de France following years of doping scandals. Indeed, last year Sir Bradley Wiggins, Froome's team-mate, lost his temper more than once when subjected to a similar interrogation.

At least Froome can seek solace within the peloton, since even his main rival Alberto Contador – the two-time winner who lost his 2010 Tour title for a doping infraction – has come out in defence of the Sky rider and has been scornful of the distrust his rival has been shown.

"There is no reason to doubt Froome," said Contador. "He is a professional rider who has been performing at a really high level all year and I think that his results are the fruits of the work he puts in and nothing else. I fully believe that he is clean. That is why the doping controls are there, isn't it?"

Froome had raced away from Contador 7.2km from the summit of Ventoux, before escaping his last remaining challenger on the mountain Nairo Quintana just as they passed the memorial to Tom Simpson, the first British rider to wear the yellow jersey and who died on the climb during the 1967 Tour.

It might only have been considered impressive had the scandal of past Tours not invited the performance to be compared to those of Lance Armstrong – the American who was stripped of his seven Tour titles for doping. It was an insinuation which was dealt with succinctly by Froome. "Lance cheated," he said. "I'm not cheating. End of story."

The tone of the conversation took the shine off the celebrations for Sky, then, with Brailsford admitting he was fed up of being made to "defend someone who has done nothing wrong". It is a practice which would seem to have become tiresome.

"Having jumped and punched the air for a second that's my five minutes of joy gone, now let's get on to the doping questions which are more important," he said. "I'm not saying they're not legitimate questions, but if there's a tinge of frustration, that's why it's there."

Brailsford has thus far refused to release Sky's training data to the public, citing a reluctance to reveal trade secrets, while also fearing that such information might be open to misinterpretation when taken out of expert hands. However, he has stated he would be willing to allow WADA officials to pore over every detail in order to satisfy the doubters.

"They can have everything we've got," he said. "They can come and live with us. They can see all of our data, have access to every single training file we've got. They can then compare that data on a consistent basis and they could then tell the world whether they think this is credible or not."

Froome's lead is a full four minutes and 14 seconds ahead of Bauke Mollema, with Contador 11 seconds further behind. The race moves now to stage 16, although the conversation remains stuck in place. "I can only be open," said Froome. "I know within myself I've trained very hard. I know what I've done to get here."