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 said he treated footballers at Premier League clubs including Chelsea, Arsenal and Leicester City along with British Tour de France cyclists, tennis players and a British boxer.
However, there is no independent evidence the sports stars received any banned treatments and the football clubs have denied the claims.
The newspaper reports 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.
London-based Dr Bonar, 38, 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.
John Whittingdale, Culture, Media and Sport Secretary, said: "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."
UKAD officials confirmed they received information from a sportsman in April and May 2014 about Dr Bonar, 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 their 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.
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."
Arsenal, Chelsea and Leicester City said they were "disappointed" by the claims and stressed their teams followed strict anti-doping protocols.
The Sunday Times report also claimed former Chelsea fitness coach Rob Brinded had "collaborated" with Bonar but it is understood he categorically denies the allegation.
In a statement, Chelsea said: "The claims The Sunday Times put to us are false and entirely without foundation.
"Chelsea Football Club has never used the services of Dr Bonar and has no knowledge or record of any of our players having been treated by him or using his services."
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.
The Press Association is attempting to contact Dr Bonar for comment.