Spanish prosecutors have opened a criminal investigation to determine whether the secretary general of Vox, a fast-rising Spanish populist party, is guilty of hate speech for warning of an 'Islamist invasion'.

The criminal inquiry, based on a complaint from a Muslim activist group, appears aimed at silencing critical discussion of Islam ahead of national elections on April 28. More broadly, however, the case poses a potentially immeasurable threat to the exercise of free speech in Spain.

Prosecutors in Valencia, the third-largest city in Spain, said that they were investigating Javier Ortega Smith (pictured), the second-ranking leader of Vox, for an alleged hate crime after they received a complaint from a Muslim group called 'Muslims Against Islamophobia'.

The founder of Muslims Against Islamophobia, Ibrahim Miguel Ángel Pérez, said that Ortega Smith's comments are 'completely untrue and undermine social peace and coexistence' by 'encouraging the creation of an atmosphere of fear and rejection towards Muslim communities.'

Prosecutors must now determine whether Ortega Smith is guilty of a hate crime as described in Article 510.1 of the Criminal Code, which establishes prison sentences of between one to four years for those found guilty of 'publicly fomenting, promoting or inciting, directly or indirectly, hate, hostility, discrimination or violence against a group [...] for racist, anti-Semitic or other motives associated with ideology, religion or beliefs.'

Ortega Smith said that he would be 'delighted' to explain to prosecutors what the 'Islamist invasion' means, namely 'the attempt to end freedoms, to end respect for family, life, women and democracy.'

If the prosecutor determines that there is some alleged crime, 'there will be no problem to explain that Europe and Spain are facing an attempted Islamist invasion because of the Europeans themselves and their erroneous policies regarding national borders and their control,' he added.

Vox, founded in December 2013 in response to the degeneration of Spanish conservatism, has been soaring in the polls — in large measure because it is filling a political vacuum created by the centre-right Popular Party (PP), which in recent years has drifted leftward and is viewed by many Spanish voters as having abandoned its role as standard bearer of conservative values.