According to a Spanish Interior Ministry statement, Villota, who is originally from Bilbao, has lived with false documents in the UK and has been "waiting for instructions" from Eta.
The Ministry says Villota was recruited in 1990 to join the legal Matalaz Command, under the Command Vizcaya.
More top news
The actress who plays the mother of murdered schoolboy Rhys Jones has told of the "responsibility" she felt in taking on the role.
The Liberal Democrat leader has been attacked after he refused to say that he does not believe gay sex is a sin.
One London Marathon runner who helped an exhausted competitor said it was "worth it" to help his rival.