In an interview with the Financial Times, Spain's Economy Minister, Luis de Guindos, suggested more money from the central government is on the table if the government in Catalonia gives up on separatism.

"Once independence plans are dropped, we can talk,” he told the newspaper, adding that: “Catalonia already has a great deal of autonomy, but we could talk about a reform of the funding system and other issues”.

He dismissed what was left of the Catalan plan for a vote on October 1 as a "pantomime".

In Barcelona, the regional economy minister, Oriol Junqueras, admitted during a TV interview on Thursday morning that the practical conditions for holding the referendum in 10 days time had been changed by police operations over the past few days.

On Thursday, the Civil Guard seized 10 million ballot papers, and had previously seized more than 1 million referendum posters and pamphlets.

The Catalan regional government was still "absolutely committed" to holding the vote, said Mr. Junqueras.

"They are punishing all of the citizens of this country and this has nothing to do with the independence of Catalonia. It goes far beyond that."

He also called on supporters of independence to keep going: "We must not let them intimidate us. We are not doing anything bad. The key is for people to keep up hope".

In a statement to the country on Wednesday night, Spanish Prime Minister Mariano Rajoy warned the Catalan government not to continue with its challenge to the Spanish Constitution, labelling it "radically anti-democratic".

"They know that this referendum cannot be held", he said: "What is at stake is not a political demand but the fundamental basis of democracy".