Great Britain hurdler Rhys Williams can return to competition with immediate effect after having his ban for a positive drugs test reduced to four months by UK Anti-Doping, his representatives have confirmed.

The Wales 400-metre hurdler tested positive in July last year for a prohibited substance contained in a contaminated supplement and was subsequently issued with a ban, the length of which was not made public.

However, his legal team have successfully argued that, although the positive test came before the introduction of the new World Anti-Doping Code on January 1 this year, Williams should be able to take advantage of new powers of discretion given to tribunals in cases where there is no significant fault or negligence on the part of the athlete.

Colin Gibson, a partner at Charles Russell Speechlys LLP who represented Williams, said in a statement: "The decision handed down by the tribunal is significant in that it is an early application of the 2015 WADC sanctions to a case under the previous rules, and because it is likely to be a benchmark for future contaminated supplement cases.

"In applying the sanctions under the 2015 Code the tribunal elected to suspend Rhys Williams for only four months which means that Rhys is able to return to competition with immediate effect."

Another Wales and Great Britain athlete, 800m runner Gareth Warburton, has also had his ban reduced to six months having failed a test in June.

Warburton's case also involved the same contaminated supplement, an energy drink which was found to contain anabolic steroid metabolites.

A statement from Warburton released by his management company read: "Both UK Anti-Doping and the NADP (National Anti-Doping Panel) reiterate that there was no intention by myself to cheat and that I could not reasonably have known that what I had used contained prohibited substances.

"Unfortunately, I have simply been an unlucky victim of a contaminated supplement, but I do take full responsibility for all substances found in my system. I am committed to drug-free sport and will work actively with the governing bodies to further educate and share what I've learnt.

"Understandably, the last six months have been extremely difficult for me and those closest to me and so I would firstly like to take this opportunity to thank my family, friends and fellow athletes for their continued support.

"As a passionate Welshman, missing out on the chance to represent my country at last year's Commonwealth Games was devastating. However, I am now looking forward to putting this difficult period behind me and getting back to what I love doing."