The ban was imposed by the British Olympic Association (BOA) because of his self-confessed past use of performance-enhancing drugs.

The judge issued his ruling this morning after spending yesterday listening to the conflicting arguments over the athlete's attempt to win an injunction suspending the bylaw before a full trial of the issues in March next year.

Mr Justice Mackay returned to the London court this morning to give his ruling to a packed courtroom and the athlete himself.

The judge said: "Many people both inside and outside sport would see this bylaw as unlawful.

"In my judgment it would take a much better case than the claimant has presented to persuade me to overturn the status quo at this stage and compel his selection for the Games."

During the hearing yesterday, the judge had commented to Jonathan Crystal, representing Chambers: "The reality is that you are saying 'put him on the plane'."

Mr Crystal, an expert in sports law, had told the judge that banning Chambers could deprive Britain of its best chance of winning a medal in the 100 metres in Beijing next month.

Chambers, 30, served a two-year suspension for using the designer steroid tetrahydrogestrinone (THG).

Mr Crystal said the BOA bylaw was unfair, contrary to competition law and an unreasonable restraint on trade.

"He represents our best chance of a podium finish in the 100 metres in Beijing," Mr Crystal said.

Chambers had already qualified to compete in the Olympic team after winning the 100 metres at the Olympic athletics trials in Birmingham last Saturday and setting his best time of the year of 10 seconds.

David Pannick QC, representing the BOA, had told the judge that Chambers "cannot show that sportsmen and women are significantly restrained in their trade by the bylaw which only concerns eligibility for an amateur event, which takes place once every four years and for which there is no prize money".

He added: "If the court were to make an order requiring the claimant to be selected, that would deprive another athlete of his place in the team, even though the legality of the rule may be upheld at a full trial."

As a self-confessed drugs cheat, Chambers was not a good example for Britain's next sports generation and the court should not force the BOA to pick him, Mr Pannick argued.

BOA chairman Lord Colin Moynihan welcomed the ruling.

Speaking outside court he said the association would continue to send a "powerful and important message" to athletes that drugs cheats would not have the honour of representing the UK.

He added that the BOA could now focus on the athletes who would be travelling to Beijing in 21 days time.