Dwain Chambers gained an unlikely ally in the battle to revive his career last night when the IAAF said that it had no problem with his controversial comeback. The vote of confidence from the sport's world governing body has added weight to the sprinter's legal position as he prepares to take UK Athletics (UKA) to court if it prevents him from competing in the trials for the World Indoor Championships.

Niels de Vos, the UKA chief executive, has stated that Chambers cannot take part in the trials because he has not taken a drugs test since November 2006 and the IAAF requires any retired athlete to be subjected to a year of tests before returning to the sport. However, he was left embarrassed by the IAAF's statement that Chambers has not officially retired. Chris Butler, the world governing body's medical and anti-doping manager, said that a retirement form from Chambers was never received. “From an anti-doping rules perspective, he is fine to continue,” he said.

While many will believe UKA's moral stance to be copper-bottomed, the legal case looks much shakier. Chambers is using Nick Collins, a Leeds-based lawyer, to press his claims, while UKA is also consulting its legal team as the matter heads for court.

Asked if Butler's remarks strengthened Chambers's case, Collins said: “One would hope so. We are still in correspondence [with UKA] and awaiting a response, but something needs to happen quickly.”

The trials begin in Sheffield on Saturday week and, unless UKA backs down, Collins will seek an injunction to allow his client to take part.

Chambers, who tested positive in 2003 for tetrahydrogestrinone (THG), insists that he never asked to be removed from the drugs-testing pool, while UKA maintains that he had retired to pursue a career in American football. The growing feeling is that Chambers will get legal backing to pursue his aim of going to the World Indoor Championships, in Valencia in March. “Technically, the IAAF are right, but we back UKA's position,” Russell Langley, of Drug-Free Sport, the anti-doping arm of UK Sport, said.

Chambers, 29, has entered the 60metres at the Birmingham Games at the National Indoor Arena on Saturday, when he will expect to run under the qualifying time of 6.9sec. That would normally guarantee entry to the trials and if Chambers wins the final in Sheffield in a qualifying time of 6.65 or under, he will have met the selection requirements for the event in Spain. However, the waters could be muddied further if UKA utilises the small print of its selection criteria, which states that athletes are “invited” to the trials and that the selection panel can “make value judgments on situations they consider to be exceptional circumstances”.

While De Vos would like to take a moral standpoint and has called for the criminalisation of performanceenhancing drugs, he is aware that that will not resolve the Chambers issue. UKA's claim that he retired does not tally with either the official forms or Chambers's remarks as he tried to move into American football. In an interview in December 2006, he said: “I plan to come back [to athletics], regardless. It's something I still have a passion for.”

Should Chambers end up in Sheffield, it will raise the prospect of an intriguing duel with Craig Pickering. The 21-year-old sprinter has called for life bans for drugs cheats and could come to UKA's aid as the last line of defence by beating Chambers and denying him a place in the Great Britain team.