Just a few weeks before the World Athletics Championships in Moscow, two top sprinters tested positive for performance enhancing drugs. Tyson Gay is the fastest man this year over 100 metres and Asafa Powell is the former world record holder. They were the biggest scalps since Ben Johnson was stripped of his Olympic gold medal in 1988. Since then sophisticated testing programmes have been set up and systems to monitor athletes' whereabouts are in place.

In this week's Report, Simon Cox examines why so few cheating athletes are being detected. He speaks to the key figures who have drawn up the most damning assessment of the anti-doping regime and the failure of individual national bodies to properly address the problem. And he travels to the German laboratory who developed a test for the latest banned drug which can still be bought legally in the UK.