The Big Question: Why has the Eta problem flared up again, and can it ever be resolved?

Why are we asking this now?

A policeman responsible for conducting anti-terrorist operations in the Basque country died on Friday when his car exploded as he started it up in a car park in Bilbao. The blast was caused by a car bomb blamed on Eta, the armed separatist group's first killing in six months, and came after it warned that it would shortly resume armed action against the Spanish government, which they describe as "fascist".

Hadn't Eta been brought into line?

That's what Spain's government keeps saying, and the organisation has suffered a number of heavy blows in the last year, with three of its top military commanders arrested in the past seven months. But what usually happens is that younger leaders step in to replace them, less experienced but more radical and more ruthless.

Friday's bomb blast came days after the Interior Minister met national, regional and local security bodies to tighten cooperation further against separatist violence.

What do Spaniards feel after four decades of Eta violence?

Every time someone is bombed or shot the whole nation goes into shock and mourning, and political life stops for several days. The Prime Minister Jose Luis Rodriguez Zapatero rushed back from an EU summit in Brussels to attend the funeral in the small Basque village of Arrigorriaga. Thousands filled the streets of Bilbao on Saturday in protest at the attack, and town halls nationwide held five minutes' silence. But then not much changes, compounding national gloom.

Inspector Puelles was a long-standing member of Spain's national police, and helped arrest scores of Eta members and sympathisers. But he was also a Basque, so his death confirmed many Spaniards in their belief that Eta are a bunch of criminals who don't mind killing their own compatriots.

Isn't this what they are?

What makes Eta more than just a terrorist gang is that they still enjoy a crucial, if dwindling, cushion of support among Basques. Radical youngsters share Eta's aspirations for Basque independence, nurtured by a grievance against hardline police tactics. Families of hundreds of Eta prisoners held in jails across Spain make up a solid core of support. In the Basque regional elections in March, the pro-Eta party was banned from standing on the grounds that it condoned violence, but tens of thousands cast blank votes in sympathy. A radical Basque party was allowed to stand in this month's European elections – after a ban was overruled in the courts – and won 140,000 votes.

Does all this make the Basque region dangerous?

Not really. Eta doesn't kill at random, it hits meticulously chosen political targets. Puelles was a an anti-terror policeman; Ignacio Uria, shot in the head last December, was a senior entrepreneur in the company building the high-speed train link from Madrid to the Basque country – a development Eta sees as an erosion of sovereignty.

Last month, Eta warned that it would resume "an effective armed political strategy". A couple of anonymous militants interviewed in the pro-Eta Basque-language newspaper Gara reckoned the organisation "had not shown a sufficiently strong line to harm the enemy". Security sources think this amounted to a warning, and a message to sympathisers, that a campaign of terror against political targets was prepared and ready to go.

So who does Eta target?

Anyone with a political or security connection to Madrid – considered the heart of the oppressive Spanish state. Basques elected a socialist-led regional government coalition in March after 30 years of rule by conservative Basque nationalists, who some believe were soft on Eta.

Patxi Lopez's new regional government promises a much harder line, and Eta apparently planned an attack to mark his investiture in April. The arrest of Eta's top military leader, Jurdan Martitegi, in France stymied that operation, but Mr Lopez's government is in their sites.

Can the government do any more?

They've tried almost everything from the carrot to the cosh, short of sending troops into the region (an option aired, then swiftly smothered, in Spain's armed forces some time back). Latterly, increased police and intelligence cooperation with France has been effective against leaders who have gone into hiding across the Pyrenees, but only optimists believe police action is enough to crush Eta for good.

When the Socialist Prime Minister Jose Luis Rodriguez Zapatero was first elected in 2005 he staked his credibility on opening a peace process, in the teeth of opposition from the conservative Popular Party. Eta called a ceasefire in March 2006, but within months hardliners complained that progress was too slow, and the ceasefire collapsed when a bomb at Madrid airport in December 2006 killed two people.

How much more independence do the Basques want?

The Basque country enjoys more autonomy than any other region in Europe, controlling taxes and police, and establishing policy on education and public media. In addition it has the widely devolved powers common to all Spanish regions. Eta says it wants an independent homeland of its historic Basque regions in neighbouring Navarra and across the border in France. Only a tiny minority support that aspiration, so it's difficult to see what further concessions might be offered that would win broad acceptance. There have been attempts to meet Eta's smaller demands – including bringing prisoners near home – but since the last ceasefire ended in 2006, everything's on ice, and no one's prepared to concede anything.

Won't politicians eventually have to sit down and negotiate with Eta?

You'd think so, but every time the government's tried to open negotiations – three times in the past 25 years – it's ended in bitterness and failure, and not always because the government made mistakes. Many Spaniards today doubt whether Eta really wants to end Europe's last armed struggle.

Eta is said to be split on the matter, with large sections of the old guard now convinced that the armed road is a dead end. But the armed faction seems in the ascendant for the moment. The government absolutely rules out talks, and Basques themselves, and Spaniards generally, who express their longing for peace in every survey going, fear dialogue and truce just gives the gunmen a chance to rearm; most people don't believe talks will solve anything.

Will Eta ever give up their struggle?

Yes

*The organisation has been hit by effective police operations, especially in France, a traditional refuge

*Many demoralised older Eta members want to end the armed struggle, saying it will never be won

*Support from ordinary Basques is waning, based on clan loyalty, rather than political conviction

No

*The ideal of Basque independence remains strong, despite the achievement of broad autonomy

*The government has used every method it can devise to crush Eta, but without success

*As long as hundreds of Eta prisoners remain in jail, their friends and family will never abandon the cause