Arturo Villanueva Arteaga, 33, expressed relief outside Belfast Crown Court after Judge Tom Burgess declared Spain's extradition warrant invalid.

Villanueva Arteaga had been free on bail since his arrest in Catholic west Belfast on April 22, six years after coming to the Northern Ireland capital.

Spain's original arrest warrant accused Villanueva Arteaga of 1994-2000 membership in a radical Basque youth group called Jarrai. Spain's Supreme Court outlawed the group in 2007, seven years after it had merged into a new youth movement called Haika. Spain said both groups were youth wings of armed group ETA.

The warrant said Villanueva Arteaga "carried out attacks against private individuals and police; organized campaigns to discredit judges and police; and encouraged that ... Basque businesses be coerced and forced to pay money if they did not want to suffer damages."

But Burgess said Spain had failed to provide any evidence to link Villanueva Arteaga to these activities. He was arrested several times in the 1990s but never charged.

Villanueva Arteaga said Spanish authorities "breach any kind of principles" when pursuing Basque separatists like himself. He denied involvement in violence, insisting he had worked "politically, peacefully and publicly in defense of Basque youth rights and Basque national rights."

Lawyers representing Spain offered no reaction. They have seven days to file an appeal.

Spain is still awaiting a verdict from Burgess on its extradition bid for a senior ETA figure, Inaki de Juana Chaos, who was arrested in Belfast in November 2008. Burgess previously has described Spain's evidence against de Juana Chaos as weak.

Since the late 1960s, ETA has killed about 800 people as part of a campaign to create an independent Basque from regions in northeast Spain and southwest France.