SPAIN's anti-austerity Podemos has backed a Scottish-style referendum for Catalonia as it seeks to take pro-independence votes.

The anti-politics party - leading the polls ahead of a general election late this year - is widely compared to Syriza, which was swept to power amid grassroots discontent in Greece on Sunday.

In stark contrast to Spain's staunchly unionist ruling Popular Party and opposition Socialists, Podemos has already declared Scotland's September 18 vote to be "political normality".

Spain has refused to allow a plebiscite on independence in Catalonia, saying this would be unconstitutional.

Now a very senior figure in its Catalan wing has said the party will campaign for a former deal between Madrid and Barcelona like the Edinburgh Agreement, the much-mooted "right to decide" of Catalan politics.

Gemma Ubasart, the favourite of eight candidates vying to be leader of Podem, on Tuesday said: "We are the only party which defends the right to decide and which has the chance to become the government of Spain."

Several leading cultural and political commentators - such as influential singer-songwriter Lluis Llach - have stressed the political similarities of Podemos in Spanish-speaking Spain and independence campaigners in Catalan and Basque lands.

However, experts in Iberia politics stress that Podemos is seen as much a threat by Catalan independent parties as by the old unionist forces.

Podemos' rise in the polls has coincided with a drop in pro-independence sentiment, according to recent polls.

Ubasart and her colleagues are just as critical and the ruling centre-right nationalists and regionalists of Catalan President Artur Mas as they are of his counterparts in Madrid.

The political scientist - a strong ally of Podemos leader Pablo Iglesias - said she specifically rejected any idea of a unilateral declaration of independence for Catalonia.

Mr Mas has avoided any legal conflict with Madrid after it blocked his proposals to hold a formal referendum on November 9 last year.

Instead, Catalonia held what amounted to a giant protest vote with most participants backing independence.

Elections are scheduled for Catalonia in September, followed by Spain-wide general election in December.

Podemos is currently securing just under 30 per cent of the vote across Spain, more than any other party but not enough to form a government on its own.

Mr Mas's CiU alliance - currently tied in Catalan opinion polls with more radical pro-independence party Esquerra Republicana - is said to be deeply cynical about Podemos' commitment to a referendum, stressing the upstart party had set no timetable.