Different countries, different histories, different legal traditions. Scotland is a nation in the British Commonwealth, not a province (shire) of the nation of England. Aragon and Catalonia did not follow the same pattern.

Catalonia had been a nation since the 10th century. Spanish gov doesn't want a referendum because their are afraid on loose....

Yes, England retained the nationalities of the kingdoms it absorbed and became a multinational state, whereas Spain followed more absolutist traditions and wanted not just fealty but complete assimilation. Scotland remained a nation after regal unification, whereas the nationhood of Catalonia is past tense, and therefore secession has significantly different legal ramifications in their respective empires.

Catalonia has never been a nation.

The problem is that for spainyards Catalonia is just the old and rich colony. And they want to continue plunde it :(

If you look at a map you will understand the reason for why spain wants to hide and prevent a referendum.

When was Catalonia colonized? Where did the settlers come from?

"Catalonia had been a nation since the 10th century."

Again, if you believe that fantasy is true, is impossible to open your eyes to reality.

Please, point to a reputable source.

UK is an union of countries. Spain is not.