Armed officers have arrested a suspected Basque separatist in Britain in connection with an attempt to assassinate Spain's King Juan Carlos in 1997, police said.
Eneko Gogeaskoetxea Arronategui, 44, was detained by armed police in the university city of Cambridge, eastern England.
He is "wanted by Spanish authorities in connection with the attempted assassination of the king of Spain, terrorism and other serious offences," Scotland Yard said in a statement.
Arronategui was apprehended on a European arrest warrant, which states he is wanted for "participation in an armed gang; attempted assassination of the king; terrorism resulting in death; possession of weapons; theft and forgery".
The offences were alleged to have taken place on October 18, 1997.
Searches were under way at a residential address and two business addresses in Cambridge.
In Madrid, Spanish Interior Minister Alfredo Perez Rubalcaba said despite the arrest there was no evidence of an ETA network in Britain.
"I do not believe that there is an ETA structure in Britain, nor do I believe that there is a specific collaboration with anyone in Britain," he told a news conference after news of the arrest.
There was no evidence pointing to such an ETA structure in Britain, Rubalcaba added.
"I think they just go to Britain because it is the closest country to them and at the same time it is separated by water, which psychologically makes it feel further away."
The interior minister said Spain had been following the operation for months since someone gave a tip-off to Arronategui's possible presence in Cambridge.
Arronategui was believed to have held a high position in ETA in 2006 and 2007 but investigators were still looking into his exact role, the minister said.
The arrest, which came a day after the arrest of ETA suspect Daniel Derguy on terrorism charges in Cahors, France, showed that members of the armed separatist group could not hide, Rubalcaba said.
"It shows two things. First, the excellent international cooperation we have with France and Britain. And second, the difficulty ETA has: wherever they go, there will always be a policeman, whatever the nationality."
Armed Basque separatist organisation ETA is considered a terrorist group by the European Union and the United States.
It has been linked with a string of assassination plots on Juan Carlos, who became king in 1975.
ETA is held responsible for nearly 830 deaths in a near-42-year campaign for independence for the Basque Country of northern Spain and southwestern France.
In January, ETA announced a permanent, verifiable ceasefire. It was rejected by Spain's government for falling short of its demands for a surrender of arms and dissolution of the band.