Has the biological passport delivered clean or confused sport?

The biological passport made its Olympic debut at London 2012 with athletics, cycling, rowing and triathlon being prioritised for long-term testing

Tired of coming second in one of the most uneven contests in sport, the anti-doping authorities gave up.

What is the point, they reasoned, of testing for drugs the cheats have swapped for ones we cannot detect?

But this was not surrender, it was an ambush.

No longer would the testers be years behind the cheats, limited to the occasional success of catching somebody too daft to stop doping in time for the evidence to disappear, or those who really had doped by accident.

From now on, they would abandon the search for specific drugs and instead establish what an athlete's normal blood values were and wait for something abnormal to happen.

For a sport losing its grip on credibility, the biological passport was viewed as cycling's saviour and was so good even Lance Armstrong said it "worked".

It was no surprise when athletics, football and tennis said they, too, would start using it.

So why are athletes, from all sports, still doping? There are 46 people currently serving bans in the UK alone.

Former Team Sky rider Jonathan Tiernan-Locke is one of them, having become the first British athlete to be sanctioned in a biological passport case that hinged on his explanation for a single abnormal test taken a week after winning the 2012 Tour of Britain.

That test, the first he would take as part of the passport programme, produced blood values that did not match four samples he provided over the course of 2013. This accumulation of data is how the experts establish what is "normal" for each athlete. In Tiernan-Locke's case, the anomaly came first.

Specifically, the test appeared to show he had either been using the blood-boosting drug EPO in the weeks before the British race, or had had a transfusion to achieve the same effect. There was, however, no "positive".

Tiernan-Locke denies any wrongdoing, saying his blood values were skewed that morning because he was recovering from a bottle of wine, half a dozen double gins and a few vodkas for the road: a night on the tiles with his girlfriend.

He says he felt so ill the following day he did not eat or drink, for fear of vomiting, which left him dehydrated when he was randomly tested the following morning.

Dr Kingsley Hampton, a consultant haematologist, told a tribunal this summer that a binge-drinking session could result in "wildly abnormal" readings. UK Anti-Doping put up two of the UCI's biological passport experts to say otherwise.

The three-man panel found the UCI experts more persuasive and, despite strong character references and no other incriminating evidence, Tiernan-Locke was given a two-year ban. He was also stripped of his Tour of Britain title, fined almost £17,500 and sacked by Team Sky.

Jonathan Tiernan-Locke riding in Great Britain colours at the 2012 World Road Race in Limburg, a day after he gave a blood sample that would ruin his career

"I try not to be bitter about it," said the 29-year-old Englishman, who won four stage races in what looked like a breakthrough season.

"I know I won those races fair and square, but I am still stunned by what happened.

"We tried to show them my bank and phone records so they could see how I simply could not have pulled off the kind of operation they were suggesting. We also asked them to re-test my Tour of Britain samples. They didn't want to know.

"The biological passport is great in principle, if it's used to identify trends, but that is not how it's being implemented."

Tiernan-Locke is one of 20 riders who have been given bans because of irregularities with their biological passport without subsequent positive tests for specific substances. The figure in track and field is even higher, with 36 athletes receiving bans since May 2012.

Some might say the evidence being used to punish offenders is only circumstantial, but even criminal law does not always need a smoking gun.

Nevertheless, it is true that the strengths of the biological passport were initially oversold, particularly by the UCI, which needed something positive, no pun intended, to deflect attention from its failure to stop a generation from doping with impunity.

This was compounded by the desire of the World Anti-Doping Agency (Wada) to justify an industry that was testing 250,000 samples a year but still needed old-fashioned confessions, police raids and whistle-blowers to take down organised doping networks.

Speed skater Claudia Pechstein, the first Winter Olympian to win medals in five straight Games, missed Vancouver 2010 because of a dispute over her blood values - she is still fighting to clear her name

One anti-doping establishment insider, who wishes to remain anonymous, told me the biological passport was misunderstood from the beginning but said that does not change the fact it is still Wada's best weapon.

Travis Tygart, the man who built the 1,000-page case against Armstrong, agrees.

"We've been real clear," the United States Anti-Doping Agency (Usada) chief executive explained. "It's not a cure-all. Not yet."

Instead, he stresses the importance of the passport's "longitudinal" approach, the repeated analysis of the same variables over time.

"It's a fantastic tool when used properly," he added. "That means you've got to do urine analysis, blood analysis, you've got to collect samples and you've got to have experts who can read them.

"From a smart-testing point of view, it's fabulous. From a detecting point of view, it's one of the tools in the toolbox."

That last point is where the debate about the biological passport is fiercest.

Nobody opposes the idea of using it to target more testing at those with suspicious blood values, but a growing number of coaches, lawyers and even scientists are uneasy about using it to sanction athletes without supporting evidence.

Dutch-based analytical chemist Klaas Faber is one of those.

Five years ago he co-authored a report that was critical of the way blood values were being interpreted and he thinks it is getting worse.

"Forensic scientists (in criminal cases) use a strong statistical model to evaluate the evidence, but anti-doping scientists have been improvising since the start," he said.

Faber blames a basic misunderstanding of probabilities, the so-called "prosecutor's fallacy", for what he describes as sport's bias against the accused.

He points to the infamous case of cycling superstar Alberto Contador as an example.

The rider claimed his positive test at the 2010 Tour de France was the result of contaminated beef.

The UCI said it was because he re-transfused some stored blood that contained traces of the steroid.

The Court of Arbitration for Sport (Cas) decided neither was likely but banned him anyway on the basis he might have taken a contaminated supplement.

Faber describes this as a "tombola" approach to justice which would not stand up in civil or criminal courts.

"Experts on both sides should provide a plausible scenario and support that with a probability, so the panel, judge or jury can take an informed decision," he added.

"But in doping cases, the prosecution experts effectively take the place of the judge. Their opinion reads like a verdict."

Czech cyclist Roman Kreuziger is the latest under the microscope thanks to a series of abnormal readings in 2011 and 2012, when he rode for the Astana team.

He was eventually blocked from riding in this year's Tour de France for his new team Tinkoff-Saxo, only for the Czech Olympic Committee to clear him in September.

Having pinned their reputations on the passport, it was no surprise when the UCI and Wada appealed against this verdict to Cas.

Tiernan-Locke had the same option. But with legal costs typically running into the hundreds of thousands, he has chosen to get on with his life.

That does not mean he is happy about the way he was left to fight for himself by Team Sky. He finds it particularly galling that the team used Dr Hampton to explain away the irregular blood values of another rider, Colombian Sergio Henao.

The biological passport is an electronic record of blood and urine tests which builds up over time to give a full picture of an athlete's blood values, particularly the oxygen-carrying red blood cells

As for Tiernan-Locke's boss at Team Sky, Sir Dave Brailsford, he admits to being uneasy about how things turned out for his former charge. He also shares some of his ex-rider's concerns about the biological passport.

"It's a very useful tool and it's been a great introduction into the anti-doping movement, but we've got to be very careful that we use it in the right way," said Brailsford.

"There are questions about how quickly we react to anomalous findings. There's also a lot of work to be done on how we interpret certain values for certain riders."

He added that the biological passport has "definitely stopped" blatant EPO abuse and blood transfusions but he wonders if the cheats are moving towards micro dosing and micro transfusions.

"Is the passport too blunt a tool to deal with that?" he said.

"Because the worst scenario is to accuse somebody who is innocent, we've got to avoid that at all costs."

That is the dilemma the authorities face.

Privately, they know some athletes are already trying to circumvent the biological passport by taking a "little and often" approach to doping. Publicly, they must continue to champion its infallibility.

There is a much-cherished ideal in law that the courts should err on the side of innocence in order to prevent the chance of the guiltless being unfairly punished.

But a cynic might argue it was that kind of thinking that got cycling, and other sports, into the mess the biological passport was supposed to clean up.