Constitutional Court Chief Judge Francisco Pérez de los Cobos. Uly Martín / EL PAÍS

The chief judge of the Constitutional Court, Francisco Pérez de los Cobos, has admitted to his judicial colleagues that he was a Popular Party card-holder when he was a magistrate at Spain's highest legal body but said he no longer pays his subscription. Documentation in the ongoing Bárcenas corruption case indicated that De los Cobos had paid the minimum annual subscription fee between 2008 and 2011, the year he was named a magistrate.

However, De los Cobos is not planning to step down and has denied the incompatibility of his post with party affiliation on the basis that the law only prohibits a magistrate from holding a position within a political group. The court backed De los Cobos on Thursday, issuing a press release stating that neither the Constitution nor laws governing the legal body "establish incompatibility for belonging to, or having belonged to, a political party."

Opposition groups have decided to wait for further details but if confirmed, the situation "will be serious," said UPyD spokesman Carlos Martínez Gorriarán.

The PP responded ironically to the matter: "At this rate voting for us will be a crime," said party heavyweight Esteban González Pons, while Martínez noted: "It's hardly surprising this happens, what with the colonization of the court by the PP and Socialists."