The Constitutional Court last Thursday suspended the referendum after a legal challenge by Prime Minister Mariano Rajoy. Police have since searched newspaper offices and printers for signs of any preparation for the referendum.

The head of Catalonia's regional government, Carles Puigdemont, told journalists on Monday: "It's not an option that the referendum won't go ahead. It's 20 days away and we've already overcome many hurdles."

Puigdemont is facing criminal charges of misuse of public money, disobedience and abuse of office for organising the referendum. He is prepared to go to prison, he has said.

A majority of Catalonia's mayors have so far said they will allow the use of municipal facilities for the vote. The mayor of Barcelona, Ada Colau, said on Monday she would do everything possible to allow people to vote but would not put civil servants' jobs at risk.

Polls have shown support for independence waning in recent years with those wanting a separate state in a minority. However, a majority of Catalans want to vote on the issue.

At a peaceful march in August, convened as a show of unity in the wake of Islamist attacks that killed 16, mostly in Barcelona, the king and Rajoy were booed and jeered by the crowds in a show of resentment towards Madrid.