FOLLOWING Paula Radcliffe's world marathon record in London 12 years ago, there was stunned surprise and incredulity. And soon the doping allegations began. It's a pattern to which two-time Tour de France winner Chris Froome and double Olympic champion Mo Farah have become accustomed.

Suspicion, disbelief, and accusation are now almost default settings after any prodigious sports feat. Ask Lance Armstrong, Usain Bolt, Marion Jones, Seb Coe, Ben Johnson, Daley Thomson, Michele Smith, Paula Radcliffe, and Linford Christie.

I reported the achievements of all of them, usually with awe and respect, occasionally with scepticism – even suspicion – but never with a direct accusation of cheating. You may have observed that all the odd-numbered people on the foregoing list are dope cheats, with the others simply the target of unfounded speculation.

Coe once introduced his son to a British journalist: "This is the man who thinks your father is a drug cheat." On no more than personal belief that Coe was too prodigious to be clean. Similar speculation attends 100m world record holder Bolt, tarnished by repeated doping test positives of Jamaican compatriots. Like Bolt, Thomson and Radcliffe, and now Froome and Farah, they have all been victims of innuendo based on rumour and hearsay.

I was grilled by a French reporter following Radcliffe's world record (2:15.25) which made her highest-ranked Brit in 2003 (males included). He repeatedly attempted to have me agree that Radcliffe must be a cheat. I insisted there was no evidence, and that her history suggested something exceptional had been possible. He was from the respected French sports paper, L'Equipe, which later published a story directly accusing Radcliffe. It ignored everything I'd said and was entirely speculation, backed by no evidence. The paper marvelled that UK media should regard her as "a snow goose", above suspicion. The incident persuaded Radcliffe to store blood samples to be analysed if and when science provides improved test technology.

L'Equipe, for so long rightly sceptical of Armstrong, are now hounding Froome.

In the absence of concrete evidence, responsible journalists must rely on instincts honed by experience. When Johnson claimed Olympic 100 metres gold and the world record in Seoul ahead of defending champion Carl Lewis, specialists were incredulous, shaking their heads at each other. Yet I can recall no accusations in print in immediate race reports.

Disbelief was suspended, just as in 2001 when Armstrong rode up Alpe d'Huez, taking 1min 59sec out of Jan Ullrich. And similarly suspended as Marion Jones accumulated an improbable catalogue of Olympic medals and world titles: so demure, so articulate, so charming. So treacherous. It was years before suspicions grew so strong that we questioned her openly, looking her in the eye. She returned the stare with no hint of anger in her denials – just feigned hurt.

A consummate actress lost to Hollywood, she passed 167 dope tests, demonstrating nothing more emphatic than the anti-doping system's inadequacy. The journalist who does not question is incompetent . . . or colluding.

The Republic of Ireland's triple Olympic swimming champion, Michelle Smith, however, stretched credibility from the outset. We did not accuse, just let readers judge from the facts: she had only squeezed into the world top 100 three years earlier and had still been outside the top 30 in her gold-medal disciplines a year before Atlanta '96. A Dutch husband and coach already serving a drug ban heightened suspicion, and few could have been surprised when she was caught two years later, adulterating her urine with so much whiskey that it would have killed her had she really consumed it.

Armstrong was the greatest offender. In 2001 he rode at the rear of the field, faking early distress on the stage which finished at the summit of Alpe d'Huez. Then his team shepherded him through the peloton to catch Ullrich. With a prolonged look over his left shoulder, Armstrong stared his rival in the eye from barely two bike lengths away, and then contemptuously shot off alone. That ride took 119 seconds out of Ullrich, and effectively won the race.

Three years later, he undid Ullrich again on this climb, now a 16-kilometre time trial. Starting two minutes behind Ivan Basso, he passed him, and proceeded to take 61 seconds out of Ullrich.

It took years to prove these feats truly were beyond human.

This was a man who had not just defied cancer but won the Tour seven times. We wanted to believe his compelling story. We wanted to believe in Christie, even in the face of his having been given "the benefit of the doubt" on a stimulant positive in 1988, when upgraded to 100m silver in Seoul. So it was ultimately no total surprise when this paper was able to reveal exclusively that Christie had been 100 times the legal limit for a banned substance.

I had been charmed by him, dined with him, enjoyed his company. And now I felt betrayed.

That's how cycling now feels. Having got it so conspicuously wrong with Armstrong, there's reluctance to risk reputations by endorsing Froome – or Farah – for fear that evidence may emerge to discredit them.

One can be forgiven mistakes in life, but not the same one twice. Hence the scepticism. I squirm at cheats I unwittingly lauded – a feeling presumably even more intense among those who authored adulatory books on cheats.

My instincts tell me to trust Froome and Farah. But that's the real iniquity of doping. The innocent suffer with the guilty.

Lord, I want to believe. Help thou my unbelief.