The amount was 40 times less than the 50 picograms which the anti-doping laboratories accredited by Wada must be able to detect.

BBC: Spanish rider Alberto Contador cleared of doping charge

In Contador's case, the amount of clenbuterol found by the Wada laboratory in Cologne was estimated to be 50 picograms (millionths of a millionth of a gram) per litre.

BBC: Ban on clenbuterol doping drug may be relaxed

However, the UCI said the concentration found by the laboratory was estimated at 50 picograms - 400 times less than anti-doping laboratories accredited by the World Anti-Doping Agency (Wada) must be able to detect.

BBC: Tour de France winner Alberto Contador tests positive