The immediate practical consequences of Catalan independence – like those of the UK crashing out of the EU without a deal – would have far-reaching implications for the region, its businesses and its people.
As with warnings of City firms fleeing a hard Brexit, industry is already alarmed: half a dozen Spanish companies, including major banks, are moving their registered head offices to guarantee access to their domestic and wider EU markets.
Despite claims by pro-independence campaigners that the EU would not want to lose a wealthy region that would rank 15th or 16th in the bloc in terms of GDP, Brussels has made clear that the region will not automatically become a member.
It would have to apply, and acceptance would require the agreement of every other EU member state – including Spain, which in 2014 threatened to veto an eventual Scottish accession bid precisely to discourage Catalan independence.
The Spanish government argues that any referendum on Catalan independence would be illegal because the country’s 1978 constitution makes no provision for a vote on self-determination.
The Spanish constitutional court, which has suspended the referendum law pushed through the Catalan parliament in September, is looking into whether the law breaches the constitution.
In March this year, the former Catalan president Artur Mas was banned from holding public office for two years after being found guilty of disobeying the constitutional court by holding a symbolic independence referendum three years ago.
Catalonia has much of the paraphernalia of statehood: it has a flag, a parliament, its own police force and broadcast regulator, and it provides some of its own public services such as healthcare and education.
But an independent Catalonia would need to establish its own central bank, inland revenue, air traffic control and defence force, all of which are currently run from Madrid – as are electricity and gas transportation and distribution.
The region’s telephone networks are run by major Spanish and foreign operators and also regulated from Madrid. Its airports are 51% owned by the Spanish state, and its railway tracks and rolling stock are operated by the state.
Catalonia’s government debt as a proportion of GDP has more than tripled since 2009, standing at €76.7bn at the end of June. Its low credit rating means it cannot borrow directly on financial markets so depends on loans from the Spanish state.
Outside the EU, Catalonia would also have to establish its own border controls and customs service. The borders between Catalonia, Spain and France would become external borders of both the EU and the passport-free Schengen zone.
Britain’s apparent inability to devise a solution to precisely this problem for the border between Northern Ireland and the Irish Republic that is practicable and that the EU will accept shows how complex such issues can rapidly become.
An independent Catalonia would need to set up its own trading standards regulators and to start negotiating its own trade agreements. Unlike Britain, it is not a member of the World Trade Organisation, putting it at an instant disadvantage.
Like British nationals, Catalans would lose their EU citizenship – but also their Spanish citizenship: if Madrid really plays it tough, they could conceivably find themselves having to apply for visas to visit not just the EU but also Spain.
As Britain’s experience with Brexit shows, leaving the EU is not a straightforward process. An independent Catalonia, however, would face an altogether greater problem: it would also have to exit the eurozone, at least temporarily.
A number of small states, including Andorra, Monaco, San Marino and Vatican City, have signed agreements with the EU to use the euro, but their economies are minuscule compared with Catalonia’s, which is nearly the size of Ireland’s.
The region’s main business lobby, Cercle d’Economia, last week said a unilateral declaration of independence “would plunge the country into an extraordinarily complex situation, with unknown, but very serious, consequences”: Brexit, but with bells on.
