"FAILSAFE STRATEGY"

The investigation was led by Canadian sports lawyer Richard McLaren, who sat on the independent commission that last year exposed doping and corruption in Russian track and field, leading to its exclusion from international competition.

The report said Deputy Sports Minister Yuri Nagornykh had been advised of every positive test across all sports from 2011 onwards and decided "who would benefit from a cover up and who would not be protected.

"The State implemented a simple failsafe strategy," it said. "If all the operational precautions to promote and permit doping by Russian athletes proved to have been ineffective for whatever reason, the laboratory provided a failsafe mechanism.

"The State had the ability to transform a positive analytical result into a negative one by ordering that the analytical process of the Moscow Laboratory be altered."

Among the hundreds of samples that disappeared were 35 from Paralympic athletes.

In Sochi itself, where international observers were scrutinising the drug tests, positive results could not simply be brushed away, so the FSB developed a method of opening urine bottles to allow samples to be swapped undetected.

Rodchenkov spoke of a clandestine night-time operation in which staff secretly took samples from the lab via a "mouse hole" cut into a wall, and replaced them with clean samples taken from the same athlete months earlier and sometimes manipulated.