United Kingdom Anti-Doping has sent two investigators to Kenya following allegations of doping at a training camp that is used by Kiwi Olympian athlete Zane Robertson and a host of British runners.
An investigation by the Sunday Times and German broadcaster ARD/WRD claims to have uncovered evidence of the use of banned blood-boosting drug EPO at the high altitude training camp in the town of Iten.
They have reported claims from Kenyan doctors that four unnamed British athletes received banned performance-enhancing drugs in the town, used as a winter base by British and other international athletes.
Robertson, a bronze medallist in the 5000 metres at the 2014 Commonwealth Games, and his twin brother Jake moved to Iten after leaving New Zealand as teenagers in 2007 to further their athletic careers.
The twins made the decision to base themselves at Iten after meeting Kenyan athletes at the 2006 world cross country championships in Japan and deciding they wanted to train with the best runners in the world.
"We are extremists and love to push our limits," said Jake at the time.
Zane moved to neighbouring Ethiopia in 2013 but still does his track training in Iten. He is among the 10 athletes named in New Zealand's track and field team for the Rio Olympics. There is no suggestion he or Jake have been using drugs in Iten.
But the Sunday Times investigation has athletics circles around the globe chattering.
UKAD chief executive Nicole Sapstead said: 'UK Anti-Doping has reviewed the evidence presented to us by the Sunday Times and it is of grave concern and of significant interest.
'We have opened an investigation and are taking the necessary steps to corroborate the evidence and investigate it further.
'Like all investigations we cannot disclose the exact details of what we are doing, as disclosing our tactics may undermine that investigation.
'However, I can confirm this evidence is being treated with the utmost importance and urgency, and two members of UKAD staff are currently in Kenya pursuing a number of lines of enquiry.'
UK Athletics (UKA) said that none of the doctors featured in the allegations were known to it or had treated its athletes.
According to the allegations, two doctors claim to have administered a series of EPO injections to a British athlete shortly before a major race.
The Sunday Times sent undercover reporters to meet the Kenyan doctors in question.
They claim to have seen medical notes that one of the Kenyan doctors proved he treated a British athlete for an injury.
One of the Kenyan doctors involved is reported to have claimed to have helped 50 athletes take performance-enhancing drugs in the past four years.
Iten plays host to performance camps for many of the world's top athletes, seeking to capitalise on the benefits of training at altitude.
Sapstead admitted UKAD had 'concerns relating to the practices and the lack of anti-doping infrastructure in a number of countries'.
She added: 'We recognise many athletes train overseas for a number of reasons such as, warmer weather or the altitude, and sometimes in countries which do not have the necessary anti-doping systems in place.
'UKAD has no power to prevent a sport training in other parts of the world and we strongly encourage every sport to carry out a risk assessment when choosing where their athletes train and to report any concerns to us.
'Whilst ultimately it is an athlete's responsibility to protect themselves from doping, it is absolutely imperative that national governing bodies of sport ensure that their athletes and coaching staff are safeguarded and are training in safe and clean environments.
'They must ensure that they are in the best possible environment to compete, and win, clean.'4
UKA insisted it was confident that elite British athletes who trained in Iten were not exposed to doping.
The governing body said it had faith in the measures it took to ensure the 'safety and security' of its athletes, but said it could not vouch for athletes it did not support who also used the training centre.
But UKA also said it would assess whether to continue using Iten as part of its annual review of its programmes.
A UKA statement said the allegations that were put to it were 'vague and unsubstantiated'.
It said: 'To be clear, none of the allegations as presented relating to British athletes accords with our experience. Nevertheless, we take any allegations of doping seriously and will as always cooperate fully with any investigation undertaken by UKAD or other anti-doping organisations.
'The UK Athletics endurance altitude training programme oversees training of athletes at altitude locations around the world. A number of British athletes have attended the high altitude training camp at Iten in the past seven years under UKA's supervision.
'We are confident that in the operation of our altitude trips, all reasonable measures are taken to ensure the safety and security of our athletes.
'Thousands of athletes from across the world chose to train in Iten because of its unique altitude benefits, with official federation team training camps alongside individual athletes travelling under their own initiative.
'Precisely because of this fact we ensure that all UKA supported athletes only train there as part of an organised and managed camp where we can be sure that they are training in a safe environment.
'Clearly we cannot comment on the conduct of athletes that are British or from other English-speaking nations that may attend the camp outside of our own performance programme.'
UKA said its next scheduled trip to Iten would not be until the new year, giving it time to review whether to continue using the camp.
'As with all performance work, our altitude and endurance programmes are subject to review on an annual basis, with more extensive reviews taking place at the end of each Olympic and Paralympic cycle,' it said.
'Our next scheduled trip to Iten would not be until the new year, which will enable us to make a fully informed decision about whether to continue at this location in future.'
The IAAF, the World Anti-Doping Agency and Athletics Kenya were asked for comment.
'We are grateful that information from the media has been shared with the organisations that are able to investigate and take any appropriate action required,' the IAAF said in a statement.
'The IAAF continues to test the elite Kenyan athletes both in and out of competition and inside and outside Kenya.
'We will continue to do this as the country works towards establishing the required anti-doping processes in line with the World Anti-Doping Code.'
- and staff reporters