A minister has ordered an urgent investigation following claims a British doctor was secretly filmed telling how he prescribed performance-enhancing drugs to sports stars.
The doctor, named by The Sunday Times as Dr Mark Bonar, claimed he treated more than 150 sportspeople with banned substances including EPO, human growth hormone and steroids, according to an investigation by the newspaper.
He allegedly claimed to have treated Premier League footballers, British Tour de France cyclists, tennis players and a British boxer with the illicit drugs, although there is no independent evidence the sports stars received any banned treatments.
However, Premier League clubs Leicester City, Arsenal and Chelsea later expressed their disappointment at the publication of doping allegations made against them which they say are "without foundation."
The Sunday Times claims the UK Anti-Doping (UKAD) watchdog was given information about the doctor's alleged doping activities two years ago but failed to take action to stop him.
Culture, Media and Sport Secretary John Whittingdale has demanded an urgent investigation into the watchdog's response.
London-based Dr Bonar denied the allegations when they were put to him by the newspaper and said he had not breached rules laid out by the General Medical Council (GMC), the body which regulates doctors.
He is facing disciplinary hearings that could see him struck off for a separate allegation of providing a patient with inadequate care, the GMC said.
Mr Whittingdale said: "Sports fans are entitled to be sure that what they are watching is true and fair with all athletes competing on a level playing field.
"Once again, I am grateful to the excellent investigative journalism by the Sunday Times for bringing these apparent abuses to light.
"I have asked for there to be an urgent independent investigation into what action was taken when these allegations were first received and what more needs to be done to ensure that British sport remains clean.
"There is no room for complacency in the fight against doping and the Government is already looking at whether existing legislation in this area goes far enough. If it becomes clear that stronger criminal sanctions are needed, then we will not hesitate to act."
Dr Bonar, 38, is alleged to have charged clients thousands of pounds for illicit drug programmes.
UKAD officials confirmed they received information from a sportsman in April and May 2014, but said the doctor fell outside their jurisdiction and they did not believe there were grounds to refer the case to the GMC.
In October 2014 the sportsman, who has not been named, supplied UKAD with "handwritten prescriptions" he said had been issued by Dr Bonar, it is claimed. The notes were given to an independent medical expert for analysis.
UKAD chief executive Nicole Sapstead said: "Following those interviews and an investigation, UKAD found that there was nothing to indicate that Dr Bonar was governed by a sport and UKAD had no other intelligence to corroborate the sportsman's allegations."
UKAD recommended the sportsman who brought the allegations to its attention gather more information and pass it on to the GMC "if appropriate".
She added: "After assessing all the evidence, as per the National Intelligence Model, UKAD did not believe that there were grounds, at that point, to refer the case to the GMC."
UKAD chairman David Kenworthy said an independent review of the allegations against it would be conducted "as soon as possible", to examine the information passed to them in 2014 and to discern if the proper procedures were followed.
He said: "UKAD is a publicly-funded body and it is correct that it be held to account for any actions it takes. That accountability rests with the independent board."
Meanwhile, the GMC confirmed that while Dr Bonar is registered with them, he does not have a current licence to practise medicine in the UK.
He is also facing disciplinary action later this month following claims he failed to take proper responsibility for a patient's care. The allegation dates back to December 2013 and relates to the care of a patient with incurable cancer. It is not linked to the doping claims.
Commenting on the doping allegations, Niall Dickson, chief executive of the GMC, said: "These are serious allegations and we will follow them up as a matter of urgency. We expect all doctors to follow our guidance -- if they fail to do so they are putting their right to practise in jeopardy.
"Dr Bonar does not currently hold a licence and is therefore unable to practise medicine in the UK. Any doctor without a licence who continues to carry out the privileged duties of a doctor is committing a serious breach of our guidance, and potentially a criminal offence."
President of the World Anti-Doping Agency (WADA) Sir Craig Reedie has backed calls for a full investigation, insisting it is difficult to apportion blame until all the evidence has been presented.
"I understand there are calls for an enquiry by the government and I am sure UK Anti-Doping (UKAD) will do their own enquiry and they will be given all the evidence so we can get to the bottom of this," he told Radio 5 Live's Sportsweek programme.
"I think it is best to wait for UKAD to do their investigation so we have full knowledge of the facts. My own thought is if they had sufficient information they would have acted. Football will want to know what has happened, details of the evidence and if there is evidence they will act on it.
"UKAD actually do a lot of testing for the football authorities. I think there is probably enough in the high-profile leagues in England, I question whether there is enough in the peripheral leagues."
A British Cycling spokesman called for the Sunday Times to disclose all the evidence it had uncovered to help in the continuing battle to combat drug cheats.
"As the governing body for cycling in this country, we are proud of the strong culture of anti-doping we have fostered and our work with UK Anti-Doping to support clean sport," he said.
"We welcome attempts by the media to uncover wrong-doing and, while it is not clear what evidence the Sunday Times team have been able to gather beyond that already published, we would urge them to share what they do have with the relevant authorities so it can be fully investigated."