Dr Wilhelm Schanzer, head of the International Olympic Committee accredited laboratory in Cologne where Christie's urine sample was sent, said the drug could not have been produced naturally in the body.

The positive sample was found to contain nandrolene at 100 times above the legal limit.

'Absolutely clear'

"Of all the nandrolene cases that we've had recently, this was one of the clearest," he said.

"It was absolutely clearly above the limit. I have no doubt that it hasn't come from indigenous production."

Christie, 39, retired from top competition two years ago. He was suspended from competition last week after testing positive for the drug at an indoor meeting in Germany.

A vociferous campaigner against drugs in sport, he has emphatically denied that he took drugs.

Asked about speculation that Christie's test had been 100 times above the legal level - around 200 nanograms per millilitre - Dr Schanzer told the Sunday Telegraph: "The figure you give is correct, I think. I know that was in the report. I wrote the report."

Christie: I'm innocent

Dr Schanzer added: "We have sometimes discussed levels when they are borderline, say four or six.

"For me to be absolutely clear the minimum is 10. Here I am absolutely clear."

Christie said after his suspension: ""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.