Y ET again, athletics is perceived to have reached a defining moment of doping crisis.

Asafa Powell, who has broken or equalled the world 100m record four times, and Tyson Gay, former world champion at both 100 and 200m, face suspension.

We have witnessed such "moments" before, first hand. It's nearly 25 years since the Olympic 100 metres champion and world record-holder Ben Johnson was exposed as a drug cheat in Seoul. It is 14 since we exclusively broke the news that the former Olympic champion Linford Christie was 200 times the legal limit for nandrolone; 13 since a tearful CJ Hunter confessed in front of his wife in Sydney that he was a drug cheat, and nine since his wife's second husband, Tim Montgomery, was implicated in the Bay Area Laboratory Co-Operative affair which led to him being stripped of his world 100m record. That bust claimed a stellar line-up, including Britain's Dwain Chambers, but most notably the wife of Hunter and Montgomery, the multiple Olympic champion, Marion Jones.

So many defining moments have taught us to be unsurprised when some figure from the pantheon is torn down and branded a cheat, while the 167 doping controls which Jones passed have taught us to be sceptical about the sport's ability to catch them. Jones was unfrocked thanks to the FBI, not doping agencies.

Ten men have run 100 metres in 9.80 seconds or faster (Usain Bolt, Tyson Gay, Yohan Blake, Asafa Powell, Nesta Carter, Maurice Greene, Justin Gatlin, Steve Mullings, Tim Montgomery and Ben Johnson) yet only the world record-holder and Olympic champion, Bolt, has escaped doping implication. The last four named have all served suspensions for steroids.

Five (Johnson, Montgomery, Powell, Greene, and Bolt) have held the world 100m record, while the first two were stripped of it. Blake was suspended for a stimulant in 2009, Carter is one of a group included with Gay and Powell in the latest round of revelations which are subject to B sample analyisis, while five-times world champion Greene (though he never failed a test) was named in a US court case as having paid $10,000 for drugs.

Inevitably, any exceptional performance is followed by innuendo and allegations of illegal enhancement. Chris Froome is currently under inquisition surrounding his Tour de France success. When Paula Radcliffe set the women's world marathon best 10 years ago, the French media was similarly sceptical. Even today, only two women have ever come within four minutes. Radcliffe stored her blood so that it might be retested with the benefit of future scientific advancement. Froome and Mo Farah should consider doing likewise.

It speaks volumes that yesterday, during a conference call with the UK performance director Neil Black, to discuss Britain's World Championship team, an appeal had to be made to lay off doping questions. Next week, we can expect more of the same ahead of the Anniversary Games. A meeting to celebrate Olympic legacy will be hijacked by a further inquisition on drugs.

Black was grilled yesterday about the meteoric breakthrough of James Dasaolu (9.91 at the British trials on Saturday). Dasaolu, 25, is a year younger than Bolt, but has been troubled by injury. In 2007 he ran 10.33 (a time beaten by only one Scot in the past 16 years) yet could finish no better than fourth at the English Under-23 Championships.

His best last year was 10.13, a modest 0.02 ahead of 2011. So how unusual is an improvement of 0.22 in one year at world level?

Not very. Bolt ran 10.03 in his first year at 100m, aged 20. The following year he clocked 9.68, breaking the world record in Beijing. Powell ran 10.02 aged 20, then 9.87 followed by 9.77 in the next two years. Gay clocked 10.08 at 22, 9.84 and then 9.77 in the following two years. Blake (runner-up to Bolt in last year's Olympics) ran 10.07 aged 19, then 9.89, 9.82, and 9.69 (second fastest ever) in the following three years.

Black said yesterday that Dasaolu's performance "was no surprise to us", adding that it was "human nature to be suspicious, but we should be hugely excited".

The trouble is that the naive excitement of fans has been overtaken by scepticism and suspicion. It is infecting parents, sponsors, TV and print media. Crediblity is haemorrhaging. Less than a year after the Olympics there were vast swathes of empty seats at the world trials in Birmingham.

Defining moment? Most definitely. Cycling was replete with defining moments long before the Armstrong affair. It has yet to live them down.

Athletics must adopt the strongest zero-tolerance stance to salvage its future. The International Association of Athletics Federations must convince the IOC to do likewise, and begin retesting the 5000 samples it holds sooner rather than later. They should re-allocate all medals and ignore perverse nonsense about limitation of action. This would allow the 2004 GB quartet, including Scotland's Lee McConnell, to receive the relay medals retained by a US team which contained a convicted cheat.

I advocate a life ban for a first offence, without reinstatement. The guilty should be air-brushed from history with forfeiture of all career medals (including those before the offence) and expunging of all pre-conviction performances from ranking lists.

Individual national bodies should be made responsible for their athletes. Any country guilty of a second doping positive by an internationally ranked competitor (say, world top 100) within a 24-month period, should be excluded from all international competition until after the next Olympics and World Championships.