Referendums are the blunt instrument of democracy, means that do not always will their expected end. Britain, surveying the inchoate aftermath of Brexit, is learning that the hard way. Catalonia may be about to learn it too.

The independence referendum that the devolved Catalan government intends to hold on 1 Octobercan be portrayed as a cry for freedom from the rule of Madrid by a suppressed nation caged within Spain. That is much, much too simple.

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There are historic reasons why many Catalans want to go their own way, reasons rooted in the old kingdoms of Spain, reasons from the years of Franco when their language was banned, as well as supposed financial grievances and a wish for ever greater autonomy. There is also a strand of emotion that, like Brexit, sees salvation in “taking control”.

If all these elements were fused into a single political force with the parliamentary domination of, say, the Scottish National party, there would be a persuasive case for holding an independence ballot, whatever Madrid and Spanish law had to say. But that is not present reality. The agglomeration of very different parties, from bourgeois conservative to leftwing republicans to anti-Europe anti-capitalists (with a touch of anarchy thrown in) commands only a narrow majority in the Barcelona Generalitat. They have little in common but their espousal of this referendum. They are a rickety coalition, just as the administration in Madrid is a queasy minority government. There is frailty, and hectic political calculation, on both sides.

The call of “Catalonia for the Catalans” has an inevitably divisive ring. Catalonia, with its bustling economy, has drawn in outsiders from the rest of Spain and a wider Europe over many decades. It speaks two languages, not one. As Josep Borrell, a Catalan, socialist and former president of the European parliament, explained recently: “Seventy-five per cent of the people whose mother tongue is Catalan support Yes and 75% of the people with other languages as their mother tongue are against independence.”

This region, and would-be country, is profoundly split: by language, by the origins of its population and, if you examine the results map from the last Generalitat elections in 2015, between country and city. The Yes campaigners sought to turn those elections into a crude plebiscite, seeking more than 50% of the vote. They fell short, though with the Trump bonus of winning power without an overall majority of votes. But failure doesn’t dampen ardour like this.

The referendum is, frankly, illegal. The highest courts in the land have ruled it unconstitutional. So the leadership’s threat to stage it regardless and declare independence two days after an assumed triumph at the ballot box is profoundly dangerous. There is, currently, no legal way of holding a vote like this, nor any legitimate preparation for holding it. Only 10% of Spaniards support the referendum. Three-quarters of the parties in the Madrid Cortes renounce it. There is no evidence in Catalonia’s own voting patterns to give it momentum. And yet the pictures of chanting crowds we see on televisions from London to Brussels would seem to argue otherwise.

No one should doubt the Yes campaign’s skill at campaigning, or using the clout of the regional government’s resources, including universities and schools, for PR advantage. But public relations can’t heal a divided region and nor, alas, can Madrid’s fumbling response to the challenge. Arresting some Catalan politicians, threatening more arrests and holding out the possibility of suspending the devolved government may be one response to this crisis. But, at that PR level, it stokes the cynical claim that, even today, Franco equals Spain and Spain equals Franco. Any hint of oppression lite can be used to advantage.

Unlike the Brexit outcome, Catalonia’s referendum will not pass democratic muster. But, like Brexit, the possibilities after secession have barely been mentioned, let alone examined. One word – Yes – seems enough. Welcome to a new land, flowing with milk and honey. But if the European Union is alarmed about Britain leaving, it is still more alarmed – from Belgium to France to Italy – about separatist movements destroying cohesion from within. And about a Spain, 40 years after democracy returned, lurching into unpredictable confrontation as other regions – the Basque country, Galicia – stage their own UDIs. There is still room for negotiation here. Madrid has already offered talks on autonomy issues. If the Catalan government can demonstrate a consistent demand and produce properly monitored plans for an eventual referendum, perhaps with a higher ceiling than 50.1%, then that is an approach that might heal the wounds – division, anger, increasing intimidation – already opening in society. The prime minister, Mariano Rajoy, for his part, should try to move cautiously, always open to compromise and using his Socialist and Ciudadanos allies as honest brokers, along with strong, clear EU intervention.

No dreams, please. Secession, in a democratic Spain inside a democratic Europe, has to be pursued calmly and honestly. You can understand the drumbeats of separation, especially in a region where the actual presence of Madrid governance on the ground in country towns and villages is already vestigial. You can also, as with Brexit, feel the tumult of economic disaster 10 years ago still making waves. But civil unrest and wild words promise only more disaster. It is time for both sides to pause and ponder the damage. It’s time to pull back.