Barcelona no longer goes to bed to the smell of smoke, the whoop of sirens or the clattering of helicopters. Three weeks after violent unrest greeted the Spanish supreme court’s decision to jail nine Catalan separatist leaders for sedition over their roles in the failed push for regional independence two years ago, the city is slowly returning to something resembling normality.

While sporadic roadblocks set up by protesters have become just another irritation of urban life and rubbish piles up on the streets after most of the bins in central Barcelona were burned on the barricades, the true impact may be more accurately measured on Sunday when Spain holds its fourth general election in as many years. The Catalan question is once again dominating the political debate and could help the far-right Vox party surge into third place, its best-ever result.

The socialist government of the caretaker prime minister, Pedro Sánchez, has sought to cool tensions while also criticising the pro-independence Catalan regional government for taking too long to condemn the violence and for continuing to peddle what it terms secessionist fantasies.

But its stance has angered rightwing Spanish parties, who have demanded a much tougher approach and attacked Sánchez for being too soft in the face of the enduring threat to Spain’s national unity.

Pablo Casado, the leader of the conservative People’s party (PP), said in a debate on Monday night that Sánchez did not believe “in the Spanish nation”, while Santiago Abascal, the Vox leader, referred to events in Catalonia as “a permanent coup d’état”.

Sánchez retaliated by laying into Casado and Albert Rivera, the leader of the centre-right Citizens party, reminding them they had both enlisted the support of Vox – the first avowedly far-right grouping to win more than a single seat in the national parliament since Spain returned to democracy after the death of Gen Francisco Franco in 1975 – to take power in regional governments, including in Andalucía and Madrid.

“You two represent the cowardly right in the face of an aggressive far right,” he said.

The five main party leaders, from left Pablo Casado of the PP, acting prime minister Pedro Sanchez of the Socialist party, Vox leader Santiago Abascal, Podemos leader Pablo Iglesias and Citizens leader Albert Rivera. Photograph: Pierre-Philippe Marcou/AFP via Getty Images

Polls suggest Sánchez’s Socialists will win the most votes on Sunday but again fall short of a majority, as it did in April’s election.

The PP appears to be bouncing back from its disastrous showing last time when it lost more than half its seats, but things look bleak for Citizens, which has lurched further to the right and which refused to help Sánchez form a government.

Its loss seems to be Vox’s gain: with support for Citizens plummeting, the far-right grouping could move past it and the anti-austerity Unidas Podemos to become the third biggest force in Spanish politics.

Quick Guide Spain's latest election Show What’s going on in Spain right now? The country is holding its fourth general election in as many years this Sunday. Although the ruling socialist party (PSOE) won the most votes in the last election seven months ago, it fell short of a majority and was unable to enlist the necessary support to form a government. Why is Spain heading to the polls so often? Spanish politics has grown increasingly fragmented and polarised over recent years. The PSOE and their conservative rivals in the People’s party (PP) ruled for decades until their duopoly was challenged by the emergence of the anti-austerity Podemos (We Can) party and the centre-right Citizens party. The political picture has been further complicated by the advent of Vox, the first far-right party to win more than a single seat in congress since Spain’s return to democracy, and by the appearance of Más País, a new leftwing party led by Iñigo Errejón, one of the founders of Podemos. That means there are now three parties chasing votes on the left, and three chasing votes on the right. What will happen on Sunday? The PSOE is once again expected to finish first, but it will almost certainly fall well short of a majority and could lose a few of the 123 seats it won last time. The PP is predicted to rally after April’s abysmal performance, Citizens to plummet, Unidas Podemos to dip slightly, and Vox to surge ahead, possibly becoming the third biggest party in congress. And then? Back to the negotiating table and a familiar sense of déjà vu. With rightwing parties unlikely to win the 176 seats needed for a majority in the 350-seat parliament between them, it will again be up the PSOE to try to cut a deal with Podemos and others to regain office. Past experiences suggest the negotiations will be long, difficult and quite possibly fruitless. Other parties may need to break the impasse by abstaining so that the PSOE can resume power as a minority government. Photograph: Marcelo del Pozo/Getty Images Europe

Three years after Podemos was widely – but incorrectly – predicted to leapfrog the Socialists to become Spain’s leading leftwing party, the talk is once again of a sorpasso (overtaking).

“It’s clear that everything that’s happened in Catalonia in reaction to the sentence has completely captured the public agenda,” said Guillem Vidal, a postdoctoral researcher at the Berlin Social Science Centre. “What it’s done, deep down, is polarise the whole national political agenda. If you look at the polls, the consequences of this level of polarisation have been the reinforcing of the parties most deeply involved in the issue.”

Vidal said both Vox and the Catalan Republican Left, the region’s more moderate pro-independence party, were likely to benefit from the current climate. He said Abascal’s participation in the party’s first debate on public television had helped normalise Vox’s narrative and allowed it to set out its stall.

Vidal added that Abascal seemed to be aiming to emulate the French far-right leader Marine Le Pen by adopting “a more chauvinist, European far-right attitude when it comes to economic protectionism”.

Earlier on Monday, Rocío Monasterio, Vox’s leader in the Madrid region, headed to a centre for unaccompanied foreign minors in Seville to argue that such young people made the streets unsafe and posed “a serious problem in our neighbourhoods”.

Rocio Monasterio and Vox leader Abascal at a rally in Madrid. Photograph: Óscar del Pozo/AFP via Getty Images

She was met with cries of “Fascists out!”. The following day, her husband, Iván Espinosa de los Monteros, a Vox spokesman, suggested “foreigners are three times more likely to commit rape … than Spaniards”.

He was speaking after Abascal falsely claimed in the debate that 70% of gang rapes in Spain were committed by foreigners. Figures from Spain’s National Institute for Statistics show that 312 Spaniards and 96 foreigners were convicted of rape last year.

Berta Barbet, a political scientist at the Autonomous University of Barcelona, said that while the tumult in Catalonia had undoubtedly favoured Vox, a sorpasso depended on rather more than a single party surging forward.

“It’s not just about Vox rising – it’s about Citizens falling,” she said. “I think Citizens’ decline has less to do with Catalonia and more to do with its ambivalent strategy over whether it’s a centrist party or not, and with its stance on negotiating with Sánchez.”

Barbet added: “It needed to decide whether it was a centrist party that could make a deal with Sánchez or whether it wanted to be to the right of everyone.”