The complaint filed with prosecutors in Madrid targets top Vox officials including leader Santiago Abascal and general secretary Javier Ortega Smith.   

In 2016, Smith was part of a group of Vox activists who spread a large Spanish flag on Gibraltar's famous cliff-faced mountain before swimming back to Spanish territory to escape arrest.

Vox became the third-largest party in Spain's parliament in a repeat general election last month, with its election manifesto calling for Madrid to intensify diplomatic efforts to return Gibraltar to Spain.

Statements made by Vox leaders including on social media had revealed “a clear strategy of disparaging the Gibraltarians and our institutions in a manner which seems clearly designed to create an atmosphere of hatred among Spaniards towards Gibraltarians,” the government of Gibraltar said.

Chief Minister Fabian Picardo said the remarks ranged from descriptions of Gibraltar as “a leech” or “a parasite”, to unfounded accusations that Spanish workers were being “held hostage” or that the territory was a den of “money launderers” and “criminals”.

“It is the language used in the 1930s against the Jews,” he told Gibraltar's parliament on Wednesday.

“We are not going to allow this to happen without being challenged.”   

The government of Gibraltar said it had also asked Spanish prosecutors to investigate an online group called “Gibraltar: Espanol”, which it described as an “echo chamber for the anti-Gibraltarian propaganda of Vox.”

It said it would also raise its concerns with the social media platforms that host the “puerile content of this group”.

'Colony of parasites'

Spain has a long-standing claim on Gibraltar, a tiny 2.6 square mile (6.8 square kilometre) rocky outcrop on the country's southern tip that was ceded to Britain in 1713. It is home to about 30,000 people.

The nationalistic, anti-Muslim and staunchly pro-Spanish unity Vox party won 52 seats in Spain's 350-seat parliament in the November 10th polls, up from 24 at its debut in April.

In a tweet sent from Vox's official Twitter account on December 14th, the party branded Gibraltar a “nest of drug trafficking, smuggling, and home to all kinds of beach bars and fronts to launder money”.

“We must end that colony of parasites. We will never give up what belongs to us,” it added.

Agustin Rosety Fernandez de Castro, a Vox MP from the southern province of Cadiz which borders Gibraltar and one of the four party leaders targeted by the criminal complaint, said Picardo “does not like the truths we tell about Gibraltar”.

“He accuses us of hate. It is not hate, it is the denunciation of the damage that the colony of Gibraltar does to our province and to our country. You're not going to shut us up, we're not afraid,” the retired general added in a tweet.

Fernandez de Castro was one of roughly 200 high-ranking, retired army officials who signed a manifesto published in July 2018 demanding respect for Spain's late dictator Francisco Franco, who in 1969 closed Gibraltar's border with Spain.

The border was only fully reopened in 1985, a decade after Franco's death.

READ MORE: Vox: the meteroric rise of Spain's far right party