UK Anti-Doping (UKAD) is under investigation by the World Anti-Doping Agency (WADA).
British Cycling has been known as Great Britain's great medal factory, winning eight gold medals at the London Olympics, the most for more than a century.
But now, further doubt is being cast upon the medals won at London 2012.
A British rider's urine sample from an out-of-competition test in late 2010 allegedly contained irregular levels of nandrolone, a banned anabolic steroid.
But remarkably, British Cycling were allowed to carry out its own investigation into the incident, according to The Mail on Sunday.
Rather than UKAD pursuing the case itself to discover the cause of the anomalous sample - as the WADA Code in place at the time dictated - the agency reportedly tipped off senior management at British Cycling. Its investigation reached no firm conclusion.
Nandrolone can be produced naturally at high levels by some people, and there have been spates of nandrolone contamination in supplements over the past few decades.
The revelations come after British Cycling's former chief doctor Richard Freeman was struck off for practising medicine.
He was found by a medical practitioners tribunal to have ordered the banned steroid testosterone knowing or believing it was to dope a rider.
A WADA spokesperson said: "Some of the information provided to WADA on this is of significant concern. We have asked our independent Intelligence and Investigations Department to look into this matter and to contact UKAD to seek further information."
The Mail On Sunday claims the anomalous sample came from one member of a high-profile group of British Olympians, a small group of whom were then asked by British Cycling to submit to private follow-up urine screening.
The newspaper claims to know the identities of the riders who were screened, and contacted them for comment. They all declined to comment on the record.
Comments
The British cycling success story is under further scrutiny after it emerged that Richard Freeman, the disgraced former doctor of both Team Sky and the British Olympic team, wanted to access athlete medical data that could have been used to warn riders about potential breaches of anti-doping rules before the 2016 Rio Games.
In one email, sent to senior members of the British Cycling hierarchy, Freeman said it was “an opportunity to assess frequency of testing and give warning of target testing”. Riders are more likely to be tested when there is intelligence they could be doping, such as producing unusual medical data.
"In March 2021, the tribunal additionally found Freeman guilty of ordering testosterone, a performance-enhancing drug restricted by World Anti-Doping Agency and UK Anti-Doping rules, for a Team Sky cyclist in 2011, "knowing or believing" it was to help dope a cyclist."
Also very interesting to note that Freeman worked as the head of medicine and head of sports science at Bolton Wanderers F.C. from 2001-09.