As far as I understand (source: discussions with Spaniards) there is no provision in Spain's law (including the constitution) for the declaration of independence of a province.
Why therefore is there a problem in that country? Everybody is free (in Western Europe at least) to declare the independence of his village / city / suburb / whatever - which does not mean that there are any legal consequences of such a declaration.
Why isn't Madrid just letting his citizens express an idea ("independence of Catalonia") in the name of freedom - but without the need to react, since this concept ("independence of a provice") does not exist in their law?
Are there any legal consequences of such a declaration of independence - which I belive must be the case, looking at the reaction of Madrid (before, during and after the referendum)