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The claims surfaced after data leaked by a whistleblower was published in The Sunday Times.

The former head of UK anti-doping, Michele Verroken, told 5 Live it was "really concerning" that people are evading detection.

"The IAAF are doing an awful lot ... what we obviously need to do is to ask is there more we could be doing? We need to use this as an opportunity to protect athletes who are drug free, and that's what concerns me most. It takes someone like a whistle blower to make some kind of activity around something which needs to be acted on."

She described the situation as a "ticking time bomb" for some athletes.

This clip was originally broadcast on the 5Live Stephen Nolan show on 1 August 2015.