The 25-year-old Scot, who won the European 200 metres title last August, faces a two-year ban if the adverse finding is upheld. But he denies taking any banned substance, and claims the positive test from a urine sample taken out of competition last month derives from another, innocent substance.
Walker said: "I have taken another substance which is not on the banned list, and which is regularly used by many athletes. I have been told it could give the same reading. I am innocent, and expect to be exonerated."
The case - and the emergence of Walker's name - came at the worst possible moment for the domestic sport, which yesterday re-launched itself in London as UK Athletics at an event attended by Tony Banks, the Minister for Sport. The occasion was due to mark a fresh start following the British Athletic Federation's lapse into receivership in October 1997.
Dave Moorcroft, chief executive of UK Athletics, acknowledged the timing was "deeply disappointing", adding: "We are here to be upbeat about the future, but we have to recognise that controversial and difficult decisions sometimes have to be faced. That is the reality of life, and sport. We will deal with this issue correctly, and - if I may use the term - positively."
Moorcroft stressed that the previous day's decision not to name Walker had stemmed from concern over the athlete's confidentiality, given that no decision on whether the sample findings require further investigation has formally been made.
He said a committee would be convened to meet "within the week", and that the intention was to let Walker know how things stood before the Bupa Grand Prix meeting on 14 February, when he is due to contest the 400 metres.
Walker's legal representative, Nick Bitel, chairman of the London Marathon, said: "Doug is deeply upset over the finding. And, I have to say, mystified."
Bitel, who has previously acted for other British athletes facing doping charges including Jason Livingston and Solomon Wariso, said a foreign athlete had been reinstated in a case that bore strong similarity to that facing Walker.
"I don't believe there has been any case similar to this in this country," Bitel said, adding that the claim was Walker's sample had shown up a metabolite of nandrolone , a banned steroid for which Butch Reynolds, the 400 metre world record holder, received a four-year ban in 1992. A metabolite is a breakdown product left in the urine sample which is evidence of what the body has metabolised.
Bitel said: "The metabolite could derive from a completely different substance. It could also be naturally occurring."
Comments given yesterday by Dr Malcolm Brown, director of medical services for UK Athletics, offered comfort to Walker. Brown explained there was more than one way of interpreting the commonly used method of measuring metabolites.
He said: "Any particular breakdown product can come from any number of parent sources. You can't know for sure what was the parent molecule."
He added that Walker's case was not a clear one. "It is not like finding a banned substance in a urine sample that has got no right to be there."
Brown stressed that an adverse report did not necessarily mean there was a doping case to answer - "if you equate one with the other, things go badly wrong... the days when things were that simplistic are over."
He cited the case of Diane Modahl, who had a four-year ban reversed on appeal. Modahl is still seeking up to pounds 500,000 in damages from the former British Athletic Federation, a claim yet to be resolved, and the new administration is aware of the need to avoid another potentially costly legal case by sticking strictly to the book.
Alan Pascoe, charged with developing the commercial side of the sport, believes Walker's difficulty will not put off potential sponsors for this season's summer events. He said: "I am sure they will see the case within the context of a sport on the upsurge."
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