Tuesday promises to be a historic day for the future of Catalonia. On that day, the president of the regional community, Carles Puigdemont, will have to bow to the most radical sector of the parliament and unilaterally declare the independence of Catalonia, or suspend this serious decision and open a process of negotiation with the central government of Madrid.

Declaring independence will definitively close the door on negotiations and allow the Spanish prime minister, Mariano Rajoy, to apply article 155 of the constitution, under which Madrid assumes control of the regional government (Generalitat) and puts its leaders outside the law, starting with Puigdemont.

Article 155, if applied, will open a situation of great tension in Barcelona. Some even speak of the first step towards a civil war, as happened in 1936 with General Franco’s uprising.

Throughout Spain, large demonstrations have been held in favour of the unity of the country and against independence. Catalonia was never an independent country. In the 1930s a popular uprising took place in favour of a republic, but the army put it down with force. The president of Catalonia at that time, Lluís Companys, was imprisoned, and then, at the end of the civil war, was shot dead by Franco in October 1940.

If Catalonia lives in a pre-civil-war climate this is due to the mistakes of the two parties in conflict. The outbreak came in June 2010 when the central government obtained from the constitutional court the rejection of a new statute of autonomy voted for by the Catalans in September 2005. If Madrid had had the wisdom of not repressing that statute of 2005, it is very possible that we would not be in this pre-war situation now.

But Catalan nationalists also have their share of responsibility from their imposition of independence through an illegal referendum, without minimum guarantees of credibility. On 1 October, more than 2 million voters (43% of the electorate) voted for independence, but that consultation was not held in regular conditions. And 57% of voters abstained from going to the polls.

Madrid made a serious mistake when it denied a new statute of autonomy granting more powers to the Generalitat.

Only negotiation can resolve the conflict. But for that it would be necessary for Puigdemont not to declare independence on Tuesday. The risk is enormous.

Manuel Ostos

Benicarló, Spain

• Greens in the European parliament share a group with the European Free Alliance (EFA), which includes a number of Catalan politicians. We share common values, particularly a commitment to the principle of self-determination. We are also committed to the peaceful resolution of conflict and have therefore been appalled by the action of the Spanish Guardia Civil. We are equally aghast by the absence of any sort of intervention by the EU (Analysis: EU must act before it is too late, 6 October).

The Greens-EFA group pressed for and secured a debate on the issue in the European parliament. In this debate we will make clear that the people of Catalonia must be able to peacefully assert their wishes for their future without being subjected to repression and attacks.

If our foreign secretary, Boris Johnson, is still capable of making any comment without inflaming an international crisis, he should also condemn unequivocally the police and state brutality meted out against peaceful protesters.

The EU has a proud history of spreading democracy across Europe. It is absolutely vital that European leaders – and the EU institutions – continue to champion and defend the principles of democratic engagement and self-determination.

As Greens we urge heads of state and the European commission to call on both sides to step back from the brink and play a mediating role in negotiating a solution that works for the people of Catalonia and the people of Spain.

Molly Scott Cato MEP

Green, South West England

• Under the escalating circumstances that your recent reports on Catalonia describe, readers may be interested in the following statement by a group of academic philosophers who work there but hold diverse views about the desirability of Catalan independence.

1. We reject the police violence against non-violent citizens used in Catalonia on 1 October 2017. Such violence is unjustified, even given the Spanish constitutional court’s judgment about the referendum’s illegality. We call on all Spanish and Catalan politicians to abstain from violence, unilateral action, provocation and manipulation. Free speech and respectful dialogue, guided by reasoned arguments and facts, must be the means by which to solve political disputes.

2. As a step towards tension reduction, we propose to the Spanish and Catalan governments that a commission be formed consisting of expert representatives of all major parties, including the opposition parties of both parliaments, with the task of building a consensus for the procedural and substantive norms for conflict reduction in this case. The commission should include experts in law, political philosophy, and conflict resolution.

3. While it is unlikely that a single set of norms will achieve universal agreement within the commission, the majority required should not merely exceed 50%. For political decisions with momentous long-term effects, agreements should require clear and significant majorities.

Victoria Camps, Jaume Casals, José Luis Martí, Teresa Marques, JJ Moreso, Genoveva Martí, Thomas Sturm, Joan Vergés Gifra, Andrew Williams

For full statement and list of co-supporters, see tinyurl.com/cataloniadeclaration

• Irish peace negotiators played a useful role in talks that led to the disarmament and political inclusion of Eta, the armed Basque separatist group. Is there scope now for Anglo-Scottish assistance in the current impasse between Barcelona and Madrid – a joint visit by Alex Salmond and David Cameron, perhaps? Arguably the breakdown in Catalonia is more serious for European cohesion than the Brexit process, and if the UK is to be a serious post-Brexit partner then Brits must start showing some statesmanship.

Richard Bourne

London

• Since Nato illegally bombed Serbia in 1999 to wrest control of Kosovo from the Balkan nation, we have witnessed a significant increase in the number of secessionist efforts around the world as borders have unravelled in Ukraine and elsewhere (Catalan president vows to press on with independence, 5 October). Western leaders should be ashamed at having encouraged the hopes of terrorists worldwide that borders can be changed and national sovereignty and international laws are meaningless if they can get Nato to support their cause. Get ready for a lot more trouble ahead.

Dr Michael Pravica

Henderson, Nevada, USA

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