(CNN) A British doctor accused of doping 150 elite athletes is denying the allegations against him, claiming they are "false and very misleading."
Mark Bonar was the subject of an investigation by The Sunday Times, which reported that he provided sports stars with banned performance-enhancing drugs.
Among his purported clients are Premier League football players, boxers, Tour de France cyclists, tennis players, bodybuilders and cricketers, the newspaper said.
Bonar responded to the allegations on Twitter.
"The @SundayTimesNews allegations are false and very misleading," he wrote. "I have never had a relationship with any premier football club or player."
The Sunday Times reported that its investigation of the doctor began with a call from a whistle-blower.
The whistle-blower -- an athlete who had reportedly been prescribed banned substances by Bonar -- received a two-year suspension after achieving some of the best times of his professional life.
The newspaper also sent reporters undercover to talk to Bonar. Their conversation at a hotel restaurant was filmed and appears to show the doctor admitting that he'd treated athletes with banned performance-enhancing drugs.
Perhaps complicating the case further, Bonar is not currently permitted to practice medicine in the UK. He does not hold a license, according to the General Medical Council.
"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," the council said in a statement.
Performance-enhancing drugs in sports
The Omniya Clinic in Knightsbridge, London, said in a statement that Bonar had rented consulting rooms at its premises to treat private patients for about 18 months.
"We have checked our records thoroughly during the period Dr. Bonar worked at Omniya and apart from the undercover athlete The Sunday Times used in its investigation, we can find absolutely no trace of a single high profile sportsman or woman, who has been treated or been seen at the clinic by Dr. Bonar," it said.
"We terminated Dr. Bonar's professional services agreement with The Omniya Clinic on Friday (April 1) upon learning from The Sunday Times that the GMC had revoked Dr. Bonar's licence to practice medicine in the UK."
The clinic said it "vigorously condemns the prescribing and use of any banned substances by professional athletes."
The Sunday Times story caught the attention of UK Culture, Media and Sport Secretary John Whittingdale. He thanked the newspaper for bringing the alleged abuse to light.
Among the reported allegations are questions about the involvement and behavior of UK Anti-Doping, or UKAD, the organization in charge of anti-doping policy in the United Kingdom.
UKAD began investigating Bonar after interviews with an athlete in April and May 2014.
The same whistle-blower who apparently spoke to The Sunday Times also spoke to UKAD in the hopes of reducing the length of his suspension.
The organization reported that it found no other intelligence to corroborate the athlete's allegations and nothing to indicate the doctor fell within its jurisdiction.
But it encouraged anyone with information on doping to reach out in confidence. UKAD also asked The Sunday Times for information it has uncovered so the organization can pursue any possible violations.
"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," Whittingdale said in a statement.
"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."