Catalonia was once a country in it's own right, combined with Spain through marriage and then conquered during the War of the Spanish Succession.
If Mayor Khan calls for a referendum he must first get it passed through Parliament, then it must be held, then acknowledged by all MP's. Then a negotiation must be held about separation from the United Kingdom, of which still owns most London institutions.
I support your right to protest to hold a referendum, I even accept your right to hold one and neither should you face persecution or prosecution from UK authorities, however making it ratified and acknowlegded by this Parliament is another. Nobody is distressed that what the Catalonia's are doing is right, wrong, legal, illegal, what is distressing everyone is Spain's attempts to prevent a non-legally binding referendum from taking place. It doesn't hurt them at all, so why are they being so heavy handed and attempting to 'prevent' an act of referendum that won't even change anything?