Spanish election: Can another vote end the political deadlock?

It was only in April that Spain held a general election in which the Socialists (PSOE) of incumbent Prime Minister Pedro Sánchez won.

And yet Spanish voters are returning to the polls on Sunday for their fourth general election in four years.

Lacking a majority, the Socialists needed the support of other parties to form a government.

Drawn-out negotiations with their most natural ally, the leftist Podemos party, descended into a public feud.

The two parties disagreed on the format of a governing partnership.

Without the support of any of the other main parliamentary forces, a September deadline came and went for Mr Sánchez to form a new administration, triggering Sunday's vote.

For more than three decades the Socialists and conservatives dominated a two-party landscape.

But in 2015, the arrival of two relatively new parties changed that: Podemos (We Can) and further to the right Ciudadanos (Citizens). A more recent surge by the far-right Vox means that there is now a five-party system on a national level.

This fragmented landscape makes the formation of governments more difficult and no party has won a parliamentary majority since the conservative Popular Party (PP) in 2011.

Polls suggest that acting Prime Minister Pedro Sánchez's Socialists, who have 123 seats, will win again, but will again fall well short of a majority.

However, much will depend on the overall balance between left and right in the 350-seat Congress.

After the last election, a left-leaning government looked feasible due to the 42 seats of Podemos and other seats held by smaller nationalist and regional parties, as well as the collapse of the main, opposition Popular Party.

Since then, yet another party has emerged: Más País (More Country), which is led by the 35-year-old former deputy leader of Podemos, Íñigo Errejón. Although it is polling in single figures and will only run in around a third of Spain's provinces, Más País is expected to take seats from both Podemos and the Socialists.

Mr Errejón has brushed aside warnings that he risks splitting - and therefore depleting - the left-wing vote. "We are going to facilitate the formation of a leftist government," he said. "We don't have to agree on everything."

However, an overall swing to the right could make a leftist government impossible, or even open the door to a right-wing administration.

This vote comes less than a month after the Spain's Supreme Court handed out lengthy jail sentences to nine Catalan independence leaders, triggering a massive backlash on the streets of cities in the north-east region, including scenes of violence.

Secessionists' anger at the court verdicts shows little sign of fading and Catalonia has dominated the election campaign. Parties on the right have been urging the government to clamp down on the independence movement by taking command of the Catalan police force, introducing direct rule, or even declaring a state of emergency.

"This is not Burkina Faso, Mr Sánchez, this is not Yemen - restore order in Catalonia," said PP leader Pablo Casado. Mr Sánchez has insisted he prefers to employ what he sees as a moderate line, saying he "does not want to throw more petrol on the fire of discord".

But although the prime minister has resisted calls to intervene in the region, he has refused to meet pro-independence Catalan president Quim Torra, unless he is more explicit with his condemnation of recent street violence and more supportive of the regional police.

With fears that pro-independence activists are planning to disrupt voting on Sunday, thousands of extra police have been deployed to the region.

The government will closely follow results in Catalonia, to see if the recent developments there have boosted support for pro-independence parties.

The Popular Party and Ciudadanos have promised economic reforms and tax cuts while warning that the slowdown Spain is seeing could lead to an economic crisis.

Vox has promised to take a tough line on illegal immigration, while Podemos has campaigned on social justice and equality.

However, the big question for many voters remains how willing parties will be to work together to break the political stalemate and form a new government.

Having suffered its worst ever general election performance in April, the PP has bounced back, according to polls, allowing it to eclipse Ciudadanos, its main competition until now on the right.

In the summer, Ciudadanos's leader Albert Rivera refused to negotiate the formation of a government with the Socialist PSOE, leading to a number of high-profile defections from his party and, polls suggest, an exodus of voters.

"Rivera dreamed of being the Spanish Macron," noted Ignacio Escolar, editor of the El Diario news site. "But right now all Rivera can aspire to... is to be a junior partner to the PP or PSOE."

Many polls show Vox surging in recent weeks. Having taken 24 seats in April and become the first far-right party to have a parliamentary presence in recent decades, Vox is now aiming to overtake both Ciudadanos and Podemos to become Spain's third political force.

Many observers believe the government's exhumation of Gen Francisco Franco from his mausoleum on 24 October has mobilised voters on the far right who feel nostalgia for the dictator.

Also, the recent turmoil in Catalonia is likely to provide a boost to the party, which has taken a particularly tough unionist line on the issue.