More than 200 blood bags at the centre of the drugs scandal were passed to the World Anti-Doping Agency (WADA) and the International Cycling Union (UCI) last July.

It followed the Madrid court's long-awaited decision to transfer the contents of the blood, plasma and red blood cells to anti-doping authorities.

Two-hundred and eleven frozen bags of blood and plasma were seized from the clinic of Spanish doctor Eufemiano Fuentes in Madrid after a police raid in 2006, with the doctor found to have facilitated blood doping to several of the world's leading cyclists.

Doping was not considered an offence in Spain at the time, with Fuentes initially given a one-year suspended sentence on public health grounds.

An initial verdict had ruled that the evidence should be destroyed but this was overturned after WADA and the UCI were among those to appeal.

The court has now clarified in a letter that the blood bags can only be used in currently existing cases against athletes, however.

With no cases reportedly open, the decision effectively means that athletes will not be named by anti-doping authorities.

"The request for the samples was not intended to discover potential athletes in order to open disciplinary proceedings against them, which was an argument put forward by the court to consider that it would be a prospective investigation," the ruling said, according to El Pais.

The clarification came after Fuentes urged for the bags to be returned to him, claiming publication of the names would breach doctor and patient confidentiality.

There is no appeal process against this decision, according to Spanish newspaper AS.

Anti-doping officials have faced significant difficulties in naming athletes as, with the case now in its 11th year, the statute of limitations has passed.

Only a small number of cyclists involved have ever been outed, including Tour de France winner Jan Ullrich of Germany, Spanish rider Alejandro Valverde and Italy's Ivan Basso.

Top players from tennis, football and other high profile sports are also alleged to have been part of a doping ring.

Operation Puerto has continued to prove detrimental to Spain’' sporting image, with the initial case harming Madrid's bid for the 2020 Olympic and Paralympic Games.

It contributed to them being eliminated in the first round of voting at the 125th International Olympic Committee (IOC) Session in Buenos Aires, after losing a run-off against Istanbul.

Japan's capital city Tokyo eventually emerged as the clear winners.