Victor Conte, the founder of the Bay Area Laboratory Co-operative (BALCO), believes clean athletes will be in the minority at this year's Olympics in Beijing.

Conte was jailed for four months for his part in the BALCO scandal in which Dwain Chambers was implicated, with the lab accused of being the source of designer steroid THG (tetrahydrogestrinone).

The drug was initially undetectable and was only discovered when a syringe containing a sample was sent anonymously to the Olympic drug-testing laboratory at the University of California Los Angeles by Trevor Graham.

Graham was the former coach of Marion Jones and ex-100 metres world record holder Tim Montgomery.

Both athletes were later banned despite never failing a drugs test.

Conte told BBC Radio Five Live: "I still believe the overwhelming majority are going to be using performance-enhancing substances.

"They use substances that are undetectable and they don't have enough testing.

"Then when athletes truly believe it is much more difficult to circumvent testing you'll see far more performances by athletes who are doing it with hard work as opposed to chemical substances."

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