Spanish security forces are claiming a major victory against the armed Basque separatist group Eta, “decapitating” the group with the arrest of its alleged leader.

In a joint anti-terrorist operation around Bordeaux, French and Spanish police seized Javier López Peña, 49, also known as Thierry, along with several other alleged senior members of the group.

Speaking during a visit to Senegal, the Spanish Interior Minister Alfredo Pérez Rubalcaba, said: “This is not just another operation. One of those arrested ... is the man who, in all probability, has the most political and military weight in the terrorist group Eta.”

The alleged head of Eta was reportedly holding a meeting with several top lieutenants when French and Spanish police raided their safe house in Bordeaux at around 11pm on Tuesday night. Though they were armed, police said, the alleged Eta militants offered no resistance.

Mr López Peña and several others were filmed being led into a police station in handcuffs, shouting slogans in Basque and, in one case, falling to the ground. Another of those arrested, Ainhoa Ozaeta, is alleged by Spain to have read out the communiqué announcing Eta’s ceasefire in March 2006.

Spain was preparing requests for the immediate extradition of two of the suspects arrested in Bordeaux, but the case of Thierry was more complex, as he is also wanted on criminal charges in France, Spanish court officials said.

Officers wearing balaclavas carried boxes of evidence with them, which reportedly included computers and other equipment. Spanish police are hoping that the hard discs will offer a treasure trove of intelligence about the outlawed group.

The arrests represent the most serious blow to Eta in more than 15 years. The militant group had been engaged in a renewed bombing campaign in an effort to show the Spanish Government that it was back in business following the collapse of peace talks last year.

The group has claimed responsibility for a truck bomb last week at the Basque town on Getxo, near Bilbao, and was blamed by authorities for a blast at a police barracks earlier this month that killed one civil guard. The group also gunned down a retired Socialist Party councillor outside his home just days before the General Election on March 9.

The alleged Eta boss had been known to the Spanish Government. He was reported to have made a surprise appearance at meeting with Spanish negotiators in December 2006, just days before the group broke its ceasefire with a huge blast at Madrid airport that killed two people and ended peace talks with the Government.

Mr López Peña is viewed as representing the hard line faction of the group that wished to break-off peace talks and return to violence in an effort to force the Government into greater concessions than it was willing to make. The gamble, however, appears to have failed, as the Government scores a series of swingeing blows against the group.

The latest arrests are only the latest – if most important – detentions of alleged Eta members since last June, when they formally abandoned talks to reach a negotiated end to their four-decade campaign of violence. Since that time, Spanish security services have secured the capture of 26 alleged Eta members from France, Canada and Mexico.

But perhaps the most worrying aspect for the group is the evident success with which French and Spanish security services are working together. Spanish security services say that France has thrown its full weight behind the fight against Eta, long viewed by successive French administrations as a purely Spanish problem. But the Sarkozy government has vowed to continue aiding Spain in its fight against Eta, cutting-off its traditional sanctuary and forcing its members to hide further afield.

Eta has killed more than 800 people in a four-decade violent campaign for an independent Basque homeland in the north of Spain and a south-western piece of France. It is classified as a terrorist group by the US, Spain and the European Union.

The French Interior Minister Michele Alliot Marie said in a statement that Lopez Pena was a “historic figure” of ETA who had been sought for over 20 years.

More than 750 suspected ETA members have been arrested since 2000. Security officials believe ETA’s strength has plummeted since 1992, when an earlier group of rebel leaders were arrested.

Ignacio Sanchez Cuenca, author of a book on the rebel group, said: “As ETA is a lot weaker than it was. The new arrests, although very important, have less effect.”

Polls show most Basques, who have their own distinct culture and language, do not seem to want independence. But the leader of Spain’s Basque regional government Juan Jose Ibarretxe is defying the Spanish government with plans to hold a referendum on whether to begin a debate on ties with Spain.

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