The independent research shows that out of 152 products tested, 10.5 per cent contained enough illegal substances to trigger a positive drug test.
The findings will be a wake-up call to British athletes who would face a two-year suspension if they tested positive for a banned substance, even if they believed the product was legal.
The research will revive memories of the 1990s when numerous British athletes tested positive for nandrolone, including Dougie Walker, Mark Richardson and Linford Christie, who has always blamed the failed test on a contaminated supplement. Under World Anti-Doping Agency rules ignorance is no defence.
Liz Yelling, who will compete in the marathon in Beijing, said: "These findings are worrying because athletes have a right to know that any supplements they use are totally clean."
The study, funded by Lucozade Sport, was carried out at the Newmarket laboratory of HFL, a leading drug-screening company. Andy Parkinson, acting director of UK Sport's anti-doping agency, said: "What this shows is that there are no guarantees when taking supplements and athletes have to be very mindful and cautious and manage all the risks that they can when deciding to use a particular supplement."
Meanwhile International Olympic Committee president Jacques Rogge says he expects up to 40 athletes to be caught doping in Beijing, compared to 26 at the 2004 Athens Games. He has based his forecast on the increased number and improved quality of urine analyses.