Richardson, the 27-year-old Commonwealth 400m silver medallist, was suspended from competition after testing positive last October.

But UK Athletics have announced he is free to compete in the British Olympic trials following fresh research into the nandrolone controversy.

Richardson said: "I am delighted to have been cleared of all charges and am looking forward to competing this summer and hopefully at the Olympic Games in Sydney."

However, the decision by UK Athletics still has to be approved by the International Amateur Athletics Federation, which could refer Richardson's case to its own arbitration panel.

He added: "I don't know what standpoint the IAAF are going to take. I'm just really happy and I'm going to take it one day at a time."

Supported

Richardson can take heart from the fact that the IAAF have supported the new research by Professor Ron Maughan and his team at Aberdeen University.

"I would particularly like to thank the members of the research project centred at Aberdeen University whose work has played a key role in the evidence presented to the panel."

The researchers' report concludes that "a combination of exercise and dietary supplements, none of which appears to contain a prohibited substance, can result in a positive nandrolone finding."

Moorcroft added: "What we want now is a full-blown project with the sufficient numbers involved and which will be scientifically validated, but that could take months rather than days."

Denied

One of the few men to have beaten world 400m record-holder Michael Johnson, Windsor runner Richardson has always denied taking any banned substances.

His training partner Mark Hylton was cleared of a similar offence last week after doubts were cast over the testing procedures in his nandrolone case.