How would the EU react at the moment of decision?

In the event of another 23-F event how would Brussels respond?

Particularly in light of the common commitment to the Petersburg tasks of the Western European Union which were subsumed into the EU's CSDP via the Lisbon Treaty. It is entirely unclear what constitutes humanitarian intervention, nonetheless the framework for common action exists. But will Brussels act when, or if, the time comes?

Or will the stand down, staring on from the sidelines?

And if instead of the sledgehammer approach of Tejero, a more astute class of military man proposes something on the lines of the 1982 coup attempt?  Predicate the crackdown on a false flag operation to implicate the "enemy." If an Atocha scale event happens in Madrid and the blame is placed on the ERC (Left Wing Catalan nationalists, remember that elements of Terra Lliure integrated into the party in the 1990s) will Brussels act if the military impose martial law in Catalonia, or throughout the country?  

Moreover, if they were smart they would eliminate the PP leadership in an operation of this sort to make independent military action more plausible.  And would the Generalitat stand aside, the Mossos do nothing as the national army moves into the region to occupy?

As much as this is, now, a dark, if distant, possibility, it seems that the sheer possibility that this might come to pass in Spain, or elsewhere, should be grounds for the EU to specify what happens if a member state government falls to military action, or otherwise ceases to be a democracy.  You would think this to be a no brainer, but all you have to do is look to the silence on Hungary with Fidesz to be worried that no action is an acceptable action for Brussels.

And I'll give my consent to any government that does not deny a man a living wage-Billy Bragg