Catalans go to the polls today in local elections that could plunge Spain into its deepest constitutional crisis since the end of the Franco dictatorship.

Polls indicate that a coalition of parties favouring independence for the region will gain a majority in the Catalan parliament.

While the elections themselves, in which as many as 5.4 million people are expected to vote, have no constitutional power to determine autonomy, the broad alliance of the left and right wing parties that favour a breakaway has defined the vote as a de facto ballot on secession.

For its part, the government in Madrid has said that it will vehemently oppose any power grab from Barcelona.

In pictures: Catalonia independence demonstrations in Spain Show all 10 1 /10 In pictures: Catalonia independence demonstrations in Spain In pictures: Catalonia independence demonstrations in Spain Spain People wave flags, that symbolize Catalonia's independence, in Barcelona AP In pictures: Catalonia independence demonstrations in Spain Spain An anti-independence Catalan holds an unconstitutional Spanish flag as he takes part in a demonstration for the unity of Spain in the centre of Barcelona during Catalonia National Day (Diada) In pictures: Catalonia independence demonstrations in Spain Spain Demonstrators gather around a ballot box during a Pro-Independence demonstration as part of the celebrations of the National Day of Catalonia in Barcelona In pictures: Catalonia independence demonstrations in Spain Spain Demonstrators march during a Pro-Independence demonstration as part of the celebrations of the National Day of Catalonia in Barcelona In pictures: Catalonia independence demonstrations in Spain Spain People stand on a balcony decorated with Catalonia flags in Barcelona In pictures: Catalonia independence demonstrations in Spain Spain A Catalan opposed to independence gives a fascist salute as he takes part in a demonstration for the unity of Spain in the centre of Barcelona during Catalonia National Day (Diada) In pictures: Catalonia independence demonstrations in Spain Spain Members of right-wing party National Alliance take part in a demonstration with a banner reading 'Against the independence manipulation of the History' during the occasion of the 'Diada' or Catalonian Day, in Barcelona In pictures: Catalonia independence demonstrations in Spain Spain A man and a girl with their faces painted with flags, that symbolizes Catalonia's independence, stand during a demonstration calling for the independence of Catalonia in Barcelona In pictures: Catalonia independence demonstrations in Spain Spain Demonstrators march holding torches during a Pro-Independence demonstration in Barcelona In pictures: Catalonia independence demonstrations in Spain Spain An aerial view of a giant Senyera (Catalan flag) formed by several thousands of demonstrators during celebrations of Catalonia National Day (Diada) in Barcelona

The regional president, Artur Mas, has intimated that even a huge turnout for the pro-independence parties would not lead to a unilateral declaration of independence – a move that will disappoint those most ardently in favour of a divorce from Madrid. Instead, he has indicated that he will use the vote to push for a binding referendum.

EU leaders have been clear that, while carefully avoiding telling Catalans which way to vote, any divorce would leave Catalonia out of the bloc and out of the euro. Any route back would involve a long accession process for the region, they say. Even the church has been lined up to make a virtue of Spanish unity. The Archbishop of Valencia, Cardinal Antonio Canizares, said that there was “no moral justification” in seeking independence. “We all need each other: unity is always better than division... let us pray for Spain, let us pray for Catalonia, let us pray for it to be faithful to its roots, for its progress, for its welfare,” he said.

Industry and leading banks have also suggested that they may withdraw from the wealthy region in the event a push for secession.