Two Spanish men who are members of the Basque separatist group Eta have been arrested in west London over alleged terrorist offences, Scotland Yard and Spanish officials say.Antonio Troitino, 55, was held over alleged offences in Spain, the Spanish interior ministry said.Ignacio Lerin, 39, was also arrested under the Extradition Act during an armed dawn raid in Hounslow.Two London addresses were being searched.The men, who remain in custody in a central London police station, are believed to have been on the run in the UK for some time, the BBC understands.Troitino had been sought since April 2011 when a Spanish court reversed its decision to release him from prison.He was convicted of 22 murders in the 1980s as a member of the Basque separatists' Madrid cell, and sentenced to more than 2,700 years in prison.However, he was released amid a storm of controversy, after 24 years in jail. The Audiencia Nacional court then revoked its decision, and an arrest warrant was issued for him.Fraud and immigration offences Troitino was not placed under surveillance after his release, and Spanish authorities suspected that he might have fled the country.A 38-year-old woman was arrested at the same premises as the men for alleged fraud offences. She remains in police custody.Two other men at the premises were arrested for alleged immigration offences.For four decades, Eta has waged a bloody campaign for independence for the seven regions in northern Spain and south-west France that Basque separatists claim as their own.The London arrests were not linked to the Olympic and Paralympic Games, which start at the end of next month, police said.