Former Olympic 100 metres champion Linford Christie has tested positive for a banned substance and has been suspended by the IAAF. Christie tested positive for metabolites of the steroid nandrolone at an indoor meeting in Dortmund, Germany, on February 13th of this year.

Christie (39) retired from serious competition in 1997 but continued to compete occasionally. The reaction of disbelieving British athletes last night was to call for an urgent investigation into drug-testing procedures. Christie is the third British athlete to test positive for the substance this year.

Nandrolone can be used to develop muscles and help training. It can appear naturally in the body, but higher levels are produced as a result of supplements. It has also been found in tennis players and footballers.

Tennis player Petr Korda had traces of the substance in a dope test carried out at Wimbledon last year. Korda, since retired, escaped a ban because a panel decided he had taken steroids unknowingly.

Christie said last night that he could not explain the traces of nandrolone in his body. He now faces a lengthy battle to clear his name and will face a tribunal made up of UK athletics officials, the sport's governing body there. The whole process could take up to six months.

He said: "I agree that there should be a full investigation into the numerous cases where metabolites of nandrolone have been found in urine samples, to establish how this could happen without the knowledge of the athlete."

The former Olympic 100-metres champion added: "I'm virtually retired. For me to take drugs at the end of my career, or when my career is finished, is stupid and ridiculous.

"When I first heard the news it was a shock. I'm innocent and I keep telling everybody I'm innocent. It sounds like the same old record but I did no wrong, so that's it."

Christie has repeatedly spoken out against drugs and last year won £40,000 in a libel case after it was alleged in a magazine article that he had taken performance-enhancing substances. In 1988, when he won the 100 metres Olympic silver medal after Canadian Ben Johnson tested positive for steroids, Christie tested positive for pseudoephendrine in Seoul but insisted it came from drinking ginseng tea. His explanation was accepted by the IOC.

Athletes have been increasingly using health supplements to enhance their performances. These are legal and are not supposed to contain any substances banned by the UK Sports Council, which is responsible for drug-testing British athletes.

But Christie said last night that he did not take any supplements and could not account for his failure of the drugs test. "I do not take any dietary supplements. I'm innocent, I walk with my head held high. I'm carrying on with my life as normal."

News of Christie's positive test comes just days after Scottish sprinter Doug Walker, the European 200-metres champion, was cleared of taking nandrolone. His lawyers claimed that he had been taking health supplements, and that the steroids could also have come as a result of eating meat from animals that had been fed them.

Nick Bitel, Walker's lawyer, said last night: "It's not just in athletics. There have been a spate of these nandrolone results recently and people do have to answer the question of why it is happening suddenly."

British athletes yesterday called for a full investigation into drug testing methods.

World triple jump record holder Jonathan Edwards said: "It just doesn't add up. There's one Spanish doctor who will not accept as positive any test related to metabolites of nandrolone, because it is so flawed. I think this is all utter nonsense and complete rubbish."

Sally Gunnell, former 400-metres Olympic champion, said: "I think they (athletes) must be thinking every time they go for a test, is this nadrolone going to be showing up again? I would like to see an investigation. I think UK Sport has to look into it."

Former Commonwealth Games champion Rob Denmark, also called for drug testing procedures to be overhauled.

"I find it very odd that Christie's failed a drugs test after he's retired," he said. "Athletes are just not confident in drugs-testing procedures after what happened with Dougie Walker. He tested positive and was then cleared. No one knows where they are from one month to the next," Denmark said.

Former 400 metres runner Derek Redmond claimed the allegations against Christie would cloud what had been a magnificent career.

"The unfortunate thing is that this puts a cloud over everything Linford has done, whether he is innocent or guilty," Redmond said. "Most people who know him a lot better than I do may say it's a load of rubbish."

"If he's found innocent he will have the problem of proving he has never done anything and if he's guilty people will say `we all knew and had known all along'."

Former British athletics coach Frank Dick, meanwhile, believes athletes could be victims of their own biologies.

"I can only think - as we have seen in recent times - that this is another very tragic accident," Dick said. "I am very clear in mind that it is possible for athletes to be taking a number of substances which on their own are quite safe, and are certainly not banned.

"But when they come together, the concoction or cocktail and how the body synthesises it is where the problem starts. The body can re-constitute certain derivatives of substances which, on the package, are not clearly derivatives. The athlete takes them and unwittingly does something illegal."

UK Athletics spokeswoman Jayne Pearce said UK Athletics had not wanted to release details of the case until after a disciplinary hearing but had been forced to issue the statement after a report in the French paper L'Equipe yesterday.