The world's anti-doping agency says they fear as many as one in 10 athletes will be cheating.
The problem for London Olympic organisers is that the drugs used have become increasingly difficult to detect in the short testing windows – so even the very best facilities are not guaranteed to prevent cheating.

150 scientists in a laboratory in Harlow , close to the Olympic, will work around the clock to process over 400 samples per day, this partnership with drug giants GlaxoSmithKline is a 30 million dollar answer to the cheats.

What the London drugs lab does is give these Games the best chance possible of keeping the number of cheats down.

Al Jazeera's Lee Wellings reports from London.