“They say there are 40% in favour and 40% against independence, but what they don’t say is that the progressive left makes up 60%.” That was the message yesterday from Xavier Domènech, candidate for the leftwing Podemos party, as he addressed a packed outdoor meeting in Barcelona ahead of this week’s defining election in Catalonia.

Speaking among palm trees and tower blocks in the working-class district of Nou Barris, Domènech called for a three-way left coalition made up of the pro-independence Esquerra Repúblicana (Republican Left), the Socialists and his own party, the Catalan version of Podemos, named Catalunya en Comú-Podem.

“We are the key, so that people don’t have to choose between one bloc or another,” said Domènech. “We are not going to play Russian roulette with our country, we will create a government that represents all Catalans,” he added, promising a new start after last October’s unilateral declaration of independence, which plunged Spain into a constitutional crisis.

There was little nationalist sentiment on display at the meeting where, rather than the ubiquitous pro-independence flags, people carried the red, gold and purple flag of the second republic that was overthrown by General Franco in 1939. For the last big meeting before Thursday’s election, Comú brought out the big guns to support Domènech, among them the Barcelona mayor, Ada Colau. She said: “People power is what counts. We are unstoppable. We know what the polls say, but we might surprise them. All the polls were against us when we were running for mayor, but we won.” She condemned “the irresponsible unilateralists who have brought nothing but pain and sorrow to Catalonia. This campaign is an opportunity to recognise that error. Never again must Catalonia be driven to the precipice.”

When Colau ran for mayor in 2015 she made it clear that she did not favour independence but instead appealed to Barcelona’s long and deep tradition of radical, communitarian politics. The message appeared to resonate. Domènech, a historian with a radical pedigree, – his father was an avant-garde conceptual artist in the 1970s and his mother an activist in the anarchist CNT union – hopes that a campaign focused on social, not sovereignty, issues will have the same resonance.

However, while this may win him votes, not all of them will be transformed into seats, as the Catalan electoral system is heavily biased in favour of rural constituencies. In rural Lleida, 20,000 votes are needed to win a seat, 46,000 to win one in Barcelona.

Pablo Iglesias, the leader of Podemos in Spain, said: “We need to stop treating the issue like it was a football match between Barça and Real Madrid. Spain ... is a complex country made up of different identities, and the issue can’t be solved with judges and the police. Spain is pluri-national.”

Before the meeting, Elisenda Alamany, number two on the Comú list of candidates, told the Observer that for the coalition to work, both Esquerra and the socialists would have to make concessions.

“Esquerra would have to renounce unilateralism and the socialists would have to renounce their support for direct rule from Madrid,” she said. “We believe we could come to an agreement based on a pact to get a binding referendum, on better self-financing, a guaranteed level of social spending and tax on the highest incomes, that is 50% on incomes above €100,000. We think we can reach a broad consensus on these issues.”

Comú would not countenance joining a coalition that included the right-wing People’s party, deposed president Carles Puigdemont’s Junts per Catalunya or the centre-right Ciutadans.

“We couldn’t support Junts per Catalunya because of its neo-liberal policies and public spending cuts but for the same reason we couldn’t support Ciutadans,” Alamany said.

“Ciutadans has benefited from a situation of polarization and has presented itself as the party that will put a stop to the independence process. They only talk about stopping the process because the reality is their social policy is the same as the Popular party. They are simply benefiting from people’s weariness with the process.”

According to the polls, Domènech’s party has been inching its way up the rankings. By law there can be no more polls now before Thursday but there remains a real chance that Comú could hold the balance of power. If they can pull it off, Catalonia may take a turn to the left, with social policy taking precedence over nationalism. If not, a hung parliament and prolonged uncertainty looks the most likely outcome.