For many sports fans the men's 100m final is the key moment of any Olympic Games, the definitive race to find the fastest man on earth.

But in 1988 at the Seoul Olympics the blue riband event became one of the most controversial races in recent memory as Canadian sprinter Ben Johnson clashed with the US superstar Carl Lewis.

David Kohn tells Adam Batstone the story of what came to be known as 'the dirtiest race in Olympic history'.