Twelve Catalan separatists went on trial today in the Spanish capital for staging a failed 2017 independence referendum that triggered a constitutional crisis and exposed rifts in a nation's identity.

The trial is unprecedented in modern Spain. Carlos Lesmes, the president of Spain's Supreme Court, characterised it as the "most important" case since the country returned to democracy in 1975.

It will be a test for the impartiality of Spain's judiciary. And, as it plays out on live television and saturates news headlines, reviving debates about democratic rights and political control, it will be a test of whether Spain's governing minority coalition can hold together.

As what is expected to be a three-month trial got underway, pro- and anti-separatist demonstrators shouted at each other outside the court, surrounded by hundreds of police.


"This is a highly politicised case," said constitutional law professor Antonios Kouroutakis, of the IE law school in Madrid. "And this is a situation where it will be very difficult for the courts to satisfy society. But this is not the primary goal of the courts - to satisfy society."

The 12 separatists - including Catalonia's former vice-president and other regional officials - stand accused of rebellion, sedition and the misuse of public funds. If convicted, they could face up to 25 years in prison. They deny the charges.

"(Self-determination) is a synonym of peace, not of war," defence lawyer Andreu Van den Eyndehe told the court in his opening statement.

In October 2017, they staged an independence referendum in open defiance of the government in Madrid and the Spanish courts.

According to their results, 90 per cent of voters supported secession - which Catalonia's regional parliament used as the basis for declaring independence. But only about 43 per cent of Catalans participated, with most of those who supported the national government's position boycotting the exercise. Opinion polls at the time suggested that Catalans were evenly split on the secession question.

European Union member states supported Spain's assertion that the referendum was illegitimate and illegal. But democracy advocates were discomforted by images of national police officers in riot gear firing rubber bullets into crowds and smashing through elementary school windows to search for ballot boxes.

The separatists now say the trial is further evidence of Spain's democracy deficit, and they have appealed to the EU in a request for clemency for the arrested officials.

Catalan leader Carles Puigdemont is not on trial, because he fled Spain in late October 2017 and has avoided extradition requests. But he continued to fan the flames from Berlin, in a news conference designed to coincide with the start of the trial.

"Democracies around the world must be inspired by the Catalan struggle for democracy," he said. "And the image of our civil and political leaders on trial concerns all who live in a stronger democracy."

"I want to ask the European Union institutions why the European Union is more concerned for what is going on in Venezuela than what is happening in Madrid today," Puigdemont said.

Even some those who did not share the aim of regional independence suggested the trial is a dangerous precedent for Spain and Europe.

"Although I am not an independence supporter, nor do I share many of the decisions of the previous Catalan government, I believe that this trial is a political fiasco, placing the space for dialogue and negotiation in danger," Barcelona Mayor Ada Colau wrote in a letter to EU leadership.

"If the trial ends in guilty verdicts and sentences, it will not help to reassess Catalonia's position within Spain, but it will instead serve to exacerbate division."

Spain's central government has been on the defensive, writing off the outrage over the Catalan trial as a "disinformation campaign." Madrid released a short video, "This is the real Spain," in which a parade of Spanish and international celebrities venerate a "great democracy." Actor Richard Gere and Michelin-starred chef Jose Andres have cameo appearances.

Spanish Prime Minister Pedro Sanchez sought to allay EU concerns during a trip to Strasbourg, France, last week. In a speech to the Council of Europe, he spoke about Spain as "a full democracy." And he visited what the Spanish Government called "the two institutions that best represent and guarantee human rights and democracy in Europe - the Council of Europe and the European Court of Human Rights."

European officials have sided with Madrid, as they did during the 2017 referendum.

Frans Timmermans, the first vice-president of the European Commission, said last week that the commission had "no criticism" of the functioning of the rule of law, democracy or human rights in Spain, when he was questioned by Catalan secessionist members of the European Parliament.

But the Catalans have made an impact with their campaign. "The pro-independence side of the trial has been more active and more successful in putting across their message," said William Chislett, a political analyst at the Elcano Royal Institute, a Madrid think-tank. "Their attempts to say that Spain is not democratic have not worked. But they raised a question mark, which has done damage."

The trial could have important repercussions in Spanish politics.

Sanchez, of the Socialist Workers' Party, became Spain's Prime Minister in June 2018, several months after the referendum crisis. But his is a minority government, and Sanchez was only able to take power by aligning with Catalan separatist factions that opposed the right-wing government of Mariano Rajoy, who had led Madrid's opposition to Catalan independence.

Given the trial, some of these Catalan factions have said they feel betrayed, and Sanchez needs their support to pass his 2019 budget in Spanish Parliament tomorrow. His opponents on the political right have seized the opportunity to attack a position of weakness, with tens of thousands marching on Monday in Madrid to demand snap elections if he fails to pass his budget.

"The strange alliance that brought Sanchez to power was always going to crumble at some point, and as far as the Catalans are concerned, it's payback time," Chislett said. He noted, however, that a potential failure by Sanchez to pass the new budget would not automatically trigger elections, and that the previous year's budget could be temporarily rolled over for longer into the year ahead.