The Spanish supreme court’s decision to imprison nine democrats and civil society leaders for organising a referendum on self-determination in Catalonia marks a new phase in the struggle for independence. Catalans have been calling on the government of Pedro Sánchez for more than a year to intervene, and attempt to bring about a peaceful resolution of the crisis. Monday’s ruling is an escalation that will ignite anger right across the region.

Answering the calls of extreme rightwing elements in Spain, the court imposed crushing prison terms on nine members of the government that I had the privilege to lead. I know these people well. They are dedicated democrats, committed to the cause of peaceful democratic change to Spain’s fragile post-Franco constitution. They include the speaker of the Catalan parliament and the presidents of the two most important non-partisan civil society organisations, Omnium and the ANC. They are all pacifists and liberals.

Some members of the government, including myself, decided to go into exile to escape the persecution, and to be able to defend the rights of Catalans more effectively. If we had remained in Spain, as this judgment proves, we too would have been subjected to an unfair trial by a politicised judiciary, prevented from refuting the false accusations against us. Instead, we have been given sanctuary in other European countries, and protected against Spain’s attempts to extradite us from Belgium, Germany and Scotland. Applications for our extradition have been refused or abandoned because the allegations are recognised as purely political. Modern pluralistic democracies protect the right to political organisation and the right to peaceful political expression and association. Yet that is precisely what our nine colleagues have been imprisoned for. What Spain condemns, European democracy absolves.

The actions of the Spanish state, its government and its judiciary strike at the heart of our democratic values at the very time that Europe needs them most. This can no longer be regarded as an internal matter for Spain, or even the institutions of the EU. It is an international concern. Earlier this year, the case of the Catalan political prisoners was brought to the United Nations by an international legal team led by Ben Emmerson QC, a British international lawyer and former UN special rapporteur on human rights. In two carefully reasoned decisions, the UN Working Group on Arbitrary Detention held that the pre-trial imprisonment of the nine politicians was a violation of international law and a clear breach of Spain’s legal obligations under the International Covenant on Civil and Political Rights. But the working group went further than that. It held that the imposition of any sentences of imprisonment at the end of the trial would violate international law. It called on Spain to release the prisoners immediately, and to conduct an independent investigation to identify those public officials responsible for the arbitrary detentions and to hold them accountable. The rule of law required no less.

Instead of heeding that warning, the Spanish authorities set about disparaging the UN, accusing the working group of bias and challenging its decision. The supreme court proceeded to ignore the UN ruling and has now imposed sentences that are designed to crush the Catalan independence movement – to break the individuals who were before the court and to instil fear in the millions of people who support them. This is the reality of modern Spanish democracy.

The supreme court allowed Vox, a neo-Francoist political party, to take an active part in the legal proceedings and to question the defendants personally. The extreme right in Spain correctly perceives Catalan independence parties as a threat. The political message throughout this process has been clear. This is the old Spain reasserting itself. Never truly committed to the human rights values of the Council of Europe and the European Union, dark forces have begun to assert themselves once more, with the full acquiescence of the government and the judiciary.

The implications for democracy will be felt well outside Spain. In August, for instance, Turkey’s minister of home affairs sought to justify the persecution of elected Kurdish officials by citing the Spanish government’s actions against pro-independence politicians in Catalonia as a precedent. By turning a blind eye to the political repression in Catalonia, the EU has given succour to the Erdoğan regime that at this very moment is killing civilians in north-eastern Syria.

Two years have passed since the repression began, since the dissolution of a democratically elected parliament and the dismissal by decree of a government with a parliamentary majority. In all this time, there has not been a single political proposal put forward by the Spanish government as a constructive alternative to the call for full independence. After four elections in as many years, the Spanish government is incapable of adopting a coherent political position, and instead is backing itself into an increasingly desperate corner.

But despite the continuing persecution of the independence movement, the pro-independence parties in Catalonia gained an unprecedented level of support in the European parliament elections held in May this year. Over the course of two years of repression, with people in prison and exile, and citizens scared of the brute force of the state, the pro-independence movement has grown ever stronger at the ballot box. It is a movement that now goes far beyond its political leadership. It spans the whole of Catalan society, and is rooted in the liberal tradition of democratic radicalism.

Monday’s judgment is a condemnation not of the individual accused, but of more than 2 million people who made the referendum a reality. The decision to imprison the political leadership for giving effect to the democratic will of the Catalan people will inevitably backfire on Spain. There is now only one possible route that the Catalan nation can follow. If Catalonia is to survive and to protect its institutions and culture, it must now become an independent state in the form of a republic. We will never back down.

• Carles Puigdemont i Casamajó is the former president of Catalonia