Catalonia continues to face a harsh crackdown on its autonomy from Madrid as the European Union keeps silent.
Mr Demesmaeker said Brussels’ inability to speak out against Spain’s behaviour could cause European democracies to “crumble.”
He said: “The EU is silent and this is really a disgrace. The whole of the EU is shameful. The EU should not stick its head in the sand anymore and it should speak up.
“This is about fundamental democratic values which are at stake.”
Speaking to BBC Newsnight, he added: “If the EU fails to defend our civil rights as EU citizens, if the EU fails to defend democratic values then our democracies will crumble.”
Mr Demesmaeker also called out EU Commissioner Jean-Claude Juncker for failing to intervene.
Mr Juncker said he had personally contacted Prime Minister Mariano Rajoy to ask the government to stop the Catalonia situation from escalating.
But he claimed Brussels could not interfere as it would only “create more chaos.”
He said: “For some time now I asked the Spanish prime minister to take initiatives so that Catalonia wouldn’t run amok. A lot of things were not done.
“I would like to explain why the commission doesn’t get involved in that. A lot of people say: ‘Juncker should get involved in that.’
“We do not do it because if we do … it will create a lot more chaos in the EU. We cannot do anything. We cannot get involved in that.”
It comes as Spain jailed eight members of the Catalan Government on charges of sedition and rebellion.
Former president Carles Puigdemont called for the release of “the legitimate government of Catalonia”, a call echoed by many supporters of the Catalan independence movement.