By Paul Moss
The World Tonight, BBC Radio 4, Bilbao
There are fears in Spain that Eta will carry out an attack soon, as the armed Basque separatists ended their ceasefire on 6 June.
Nationalists were angry when some of their candidates were banned
On Thursday, Spanish police found 130kg (285 pounds) of explosives in a car parked in the town of Ayamonte, near the Portuguese border. Police said they suspected Eta.
The armed militants continue to enjoy small, but not insignificant, support in the Basque Country - and you have to be careful what words you use.
At a political demonstration some 32km (20 miles) from Bilbao, I mentioned to one protester that this was my first time in the region. "But I've been to Spain many times before," I said.
With a face that looked about as cheerful as an undertaker's, she corrected my mistake: "You're not in Spain - you're in the Basque Country."
This was more than a technical matter. The demonstration was to show support for Eta prisoners, members of a movement that has killed more than 800 people in the past three decades.
It was a friendly, jovial affair, with entertainment provided by local musicians playing traditional Basque instruments.
But the cause itself is far from frivolous. People applauded at video footage of Eta "heroes", some of whom have planted car bombs, or shot policemen.
Eta has been fighting for a Basque state since the late 1960s
"They are not killers," my new-found geography teacher insisted. "They are people fighting for a cause - to have an independent Basque state. It's the same as the IRA, the same commitment."
Many protesters talked about the oppression suffered by Basques under the former dictatorship of Gen Franco.
I pointed out that the Generalissimo had been dead for more than three decades, and that since then, Basques had enjoyed plenty of regional automony, with their language used in schools and universities. But the argument cut little ice with the protesters.
"The transition from dictatorship to so-called democracy did not solve the Basque situation," another told me. "We still do not have the right to vote for our own future."
It is a sore point here. The Spanish constitution describes the state as indivisible, and explicitly rules out referendums from regions that want to secede. When the constitution was put to a vote, only a minority of Basques supported it, but across Spain it got the thumbs-up, so Basques were stuck with it.
"We are not fighting for independence," the Basque nationalist leader Fernando Barrena insisted. "We are fighting for democracy."
Basque editor Martxelo Otamendi accuses Spanish police of torture
Mr Barrena is one of the leaders of Batasuna, the banned political party that supports Eta's aims, and which refuses to condemn its violence.
I asked how he could justify the bombing of civilians. Careful not explicitly to endorse Eta, he just suggested that when democratic means are ruled out, violence will always be "a temptation".
But for many Batasuna supporters, it is Basque culture and identity that seems to motivate them, rather than the matter of constitutional change.
"I want the Basques to be represented in the World Cup", a lawyer told me, "we want to compete in the Eurovision Song Contest, as Basques, not as Spain". He was also campaigning to address local courts in Basque, rather than being forced to use English.
Yet others claim more serious grievances with the Spanish state.
Martxelo Otamendi is editor of the world's only entirely Basque-language newspaper, Berria. The last Basque newspaper he ran was closed down by the government three years ago, for allegedly supporting Eta and its cause. Martxelo himself was arrested, and under Spain's anti-terrorist laws, he was held incommunicado for five days, unable to contact a lawyer. During that time, he says he was tortured.
"I was not allowed to sleep for the first three days," he told me. "They were making me do physical exercises naked. They covered my head with plastic, and when I tried to breathe, it went in my nose and mouth. I thought I was going to die."
Martxelo was released, and has never been convicted on any charge. Since then, Amnesty International and the United Nations rapporteur on human rights have both condemned torture in Spanish police cells.
The Spanish government denies it happens, but Martxelo is convinced it is widespread. "The more they torture Basques," he warned, "the more young people will think they have no human rights here, so they will decide to join the struggle, and fight against Spain."
The World Tonight is broadcast at 2100-2145 GMT on BBC Radio 4 on weekdays