A minister has ordered an urgent investigation after the Sunday Times Insight team filmed a British doctor describe 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.
And London-based Dr Bonar, 38, denied the allegations in a series of messages posted on what appears to be his Twitter account.
In one he wrote: "The @SundayTimesNews allegations are false and very misleading. I have never had a relationship with any premier football club or player."
He also denied prescribing hormone replacement therapy to sportsmen to enhance their performance, writing: "I have never prescribed Androgen therapy for the purpose of performance enhancement. I treat symptomatic men with low test levels."
Dr Bonar, 38, has insisted he has not breached rules laid out by the General Medical Council (GMC), the body which regulates doctors.
The GMC has confirmed that while Dr Bonar is registered with them, he does not have a current licence to practise medicine in the UK.
The Sunday Times 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.
Meanwhile, it has emerged that Dr Bonar 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 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.
Nicole Sapstead, UKAD chief executive, 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 the organisation in 2014 and to discern if the proper procedures were followed.
Dr Bonar is also facing disciplinary action later this month following separate 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 Omniya Clinic in Knightsbridge, west London, where the doctor rented consulting rooms to treat his private patients, said it ended his professional services agreement on Friday after learning he does not hold a current licence.
The Sunday Times report also claimed former Chelsea fitness coach Rob Brinded had "collaborated" with Dr Bonar, but in a statement he distanced himself from the doctor.
He said: "I am a peak performance specialist and I work with a number of high profile athletes. In January I was invited to an interview by Dr Mark Bonar with an 'investor', who I now know to be a Sunday Times journalist.
"I was told that it was to discuss my involvement with a team of consultants, one of whom was Dr Bonar, in a new, peak performance project. The project apparently involved eight athletes who were trying to make the Olympic squad and I was told that my role would be to work on the athletes' mindset and remove any negative beliefs holding them back from success."
In the statement, issued through his solicitors, Mr Brinded alleged: "Following this interview and one subsequent meeting I decided that I did not want to be involved in the project because Dr Bonar made a number of statements to the 'investor' which I knew to be untrue.
"In addition, it became apparent that the project was focused on the use of performance-enhancing drugs. I made no further contact with Dr Bonar or the 'investor'.
"I do not and have not ever worked or collaborated with Dr Bonar. I have never referred any athletes to him and, to the best of my knowledge, none of my clients, athletes or otherwise take performance enhancing drugs.
"Certain comments have also been attributed to me regarding Chelsea Football Club. I categorically deny that I have ever said that anyone at Chelsea Football Club took performance enhancing drugs. "