The man tasked with eliminating drug cheats says criminal gangs now control a quarter of all world professional sport.

David Howman, director-general of the World Anti-Doping Agency, called for everyone involved in the fight against sports corruption to band together to ensure the "bad guys" don't win.

"The biggest threat to sport is organised crime," Howman told delegates in London for a conference on securing sport.

"Don't let us compartmentalise it into match-fixing or bribery, it's organised crime.

"And I think, now, organised crime controls at least 25 per cent of world sport in one way or another."

Howman said those who were distributing drugs, steroids, HGH (Human Growth Hormone) and erythropoietin (EPO) and so on, are the same characters who corrupt athletes and pay money to fix games.

"They're the same bad guys," he told delegates.

"Now, the good guys have to prevail. Who are the good guys? Let's get them together and make sure they can work out a plan.

"Because, otherwise, the bad guys are going to win."