Athletes were given DeltaG, an energy boosting drink, despite doubts about whether it was within anti-doping rules and what side effects could be suffered by those taking it, as reported by a Mail on Sunday investigation.

Documents obtained by the newspaper show that 91 elite level athletes across eight Olympic sports were given the substance ahead of the London 2012 Games.

The substance, a synthetic version of a naturally occurring body acid called ketones, was originally developed by scientists at Oxford University, and was presented to athletes in the form of a drink as part of the Ketone Ester project.

Ketone ester became commercially available in 2018, with UK Sport's funded research project into the substance beginning in 2011.

In a statement UK Sport said: "The Ketone Ester project received independent ethical approval from the Research Advisory Group in January 2012.

"Additionally, UK Anti-Doping (UKAD) confirmed in writing, after seeking clarification from the World Anti-Doping Agency, (WADA), that WADA had no reason to consider such substances as banned under the 2011 List of Prohibited Substances and Methods.

"From the outset, this study stated it complies, and at all times will comply, with the Declaration of Helsinki developed by the World Medical Association as a statement of ethical principles to provide guidance to physicians and other participants in medical research to promote and safeguard the health of the people involved.

"It declares that the well-being of the human subject should take precedence over the interests of science and society."

Ketone supplements do not feature on WADA's list of prohibited substances and methods, however WADA told insidethegames  that they would advise extreme caution in relation to supplement use by athletes.

"The use of any supplements by athletes is a concern because, in many countries, the manufacturing and labelling of supplements may not follow strict rules, which may lead to a supplement containing a substance that is prohibited under anti-doping regulations," said WADA.

"This may happen for a variety of reasons including deliberate addition or contamination.

"A significant number of positive tests have been attributed to the use of supplements and taking a poorly labelled supplement is not an adequate defence in a doping hearing."

Documents obtained as part of the newspaper investigation showed that more than 40 per cent of athletes ended up with side-effects after taking DeltaG, including vomiting and gastrointestinal upsets, with 28 individuals stopping taking the substance for this reason. 

A further 24 later withdrew from the scheme because they believed they were not getting any benefit from taking the substance.

The investigation revealed that athletes applying to take part in the project had to sign a participant information sheet where UK Sport excluded itself of all responsibilities for athletes taking ketone ester.

This meant that if athletes failed a drugs test after taking the substance they would be the ones at fault.

Athletes also had to sign a document accepting that there was a risk to participating in the study, and accepting that those running the project could not be held liable over the risks.

Finally, athletes using DeltaG were made to sign a non-disclosure agreement meaning they could not speak about this project to anyone outside their research team or peer group.

According to the investigation, UK Sport also prepared a communications strategy in case the project was leaked to the media ahead of the London 2012 Olympics, in order to guard against what the organisation described as "negative perceptions and publicity" in relation to an "unfair competitive edge."

A confidential so-called "road map" obtained as part of the investigation stated: "The UK Sport aim is to implement the use of DeltaG with targeted athletes and sports in the period leading into and during London 2012 with events greater than five minutes’ duration and multi-event athletes. 

"These sports include cycling, hockey, sailing, athletics, swimming, modern pentathlon and select others.’"

London 2012 is Britain's most successful ever Olympic Games, with the host nation winning a total of 65 medals - 29 gold, 17 silver and 19 bronze.

UK Sport said in a statement: "Any research project funded by UK Sport investment includes a participant consent form to ensure it operates with full transparency with regards to any risks to participants, and also for the purpose of full disclosure. 

"Participating athletes agree they have been provided with full details of the study and have had the opportunity to raise and discuss questions with a named researcher. 

"Athletes are not put under pressure from UK Sport to take part in any research project or to provide their consent, and may withdraw at any time.

 "UK Sport is fully committed to developing a high performance culture that is truly inspirational and one that will set us apart from our global competitors – but UK Sport will never seek to win medals at any cost."