The Spanish government has issued a final warning to Catalan leaders – abandon independence or we will take your regional autonomy away.
That process could begin on Thursday with a move to invoke a never-before-used part of the Spanish Constitution – Article 155.
It says in its two brief paragraphs: “If a self-governing community… acts in a way that is seriously prejudicial to the general interest of Spain, the Government… can take all measures necessary to… protect the above mentioned interests.”
Teresa Freixes, one of the top experts on Spanish constitutional law, told Sky News: “The constitution doesn’t specify what measures to take, it says to take the necessary measures and that’s up to the government to propose and put them to the senate.
“One possible option is that someone substitutes for the Catalan government, authorities named by the central government, and it could be that they dissolve the Catalan parliament to call fresh elections.”
That would mean Catalan leader Carles Puigdemont and other secessionist leaders being ousted – a move which would provoke fury and celebration in equal measures in a region which is genuinely divided about independence.
Ms Freixes said: “It’s also possible to take measures over specific administrative functions – for example the police, around the finance portfolio, about education, in short, any policy area.”
The Catalan regional police – the Mossos – whose head is accused of sedition for failing to do enough to prevent the independence referendum on 1 October, are certain to come in for attention.
If the Madrid government decided to impose direct rule on Catalonia it needs to be sure the police obey orders from Madrid.
Ms Freixes explained: “The control of the police is a very important matter in an issue like this.
“Why? Well because – as the press have reported – there is a segment of the Mossos who could be supporting the independence of Catalonia and they could put themselves against the measures the Spanish government wants to take.
“Clearly the police are an armed body and if the police don’t obey the government in its command – and in this case it would legally be the Spanish government – well then we have a problem.
“So from that it seems one of the measures that could be taken would be the control of the autonomous police.”
Many in Catalonia fear the return of thousands of national police to the streets. They faced widespread condemnation for their aggressive actions on the day of the referendum.
And Spanish Prime Minister Mariano Rajoy faced a backlash himself as a result.
Many wonder how far he is prepared to go now using a provision which seems to rule out very little.
He does have to get the backing of the senate to use any measure but he has a strong majority.
Teresa Freixes believes he will be careful.
“Knowing a bit about how the character’s (Rajoy’s) psychology, he’s a very cautious person in everything he does,” she said.
“He doesn’t normally rush in like a bull in a china shop, he moves gradually.
“I get the impression this could start with concrete proposals and then as the issue develops he could add more, because the constitution doesn’t say all the measures must be adopted at the same session.
“You could pass some measures for the first step and then as it evolves you could continue with them or not.
“What is clear too is that there will need to be a time limit. Because it doesn’t seem to me possible to have an unlimited suspension of a certain competency in an autonomous community.”
She predicts that any dramatic changes will take time – days certainly – to get started as the Spanish senate will have to vote.
But even announcing an intention to invoke a provision which takes away the autonomy one of Spain’s self-governing regions is a dramatic step.
It is a sign that the “cautious” Mr Rajoy feels there is no other way out of the biggest constitutional crisis to confront any Spanish leader in decades.