A Greek criminal prosecutor has launched an investigation after a report on Channel 4 News showed a member of the neo-Nazi Golden Dawn party threatening to turn immigrants into soap.

The investigation was opened after the Greek anti-racist crime unit referred the news report to the criminal prosecutor.

The film – which was broadcast on Channel 4 News on 5 March – was shot by Konstantinos Georgousis, with the full knowledge of the members, after spending a month filming far-right Golden Dawn party on the streets of Athens.

In the film, Alexandros Plomaritis, a 44-year-old who ran for parliament for the party in last year’s election, said: “We are ready to open the ovens. We will turn them into soap … to wash cars and pavements. We will make lamps from their skin.”

Plomaritis was filmed ahead of the Greek election, and the footage also showed members of the Golden Dawn party talking openly about beating up illegal immigrants.

In a statement on its website, Golden Dawn dismissed the film, saying:

“Another shocking documentary about the illegal and murderous activities of Golden Dawn comes to light from the prestigious British Channel 4 â?¦ Foreign journalists arrived secrectly in a cafe in St. Panteleimonas to uncover the crimes against humanity perpetrated by the Golden Dawn. The regulars (one of whom was our candidate in previous elections) joke with them for hours without being informed that they are being recorded with a hidden camera (a crime!).”

However the film includes a scene in which a party member encourages a passing Bangladeshi family to pose for the camera with him on the pavement.

Elsewhere the party’s statement also refers to a previous filmed investigation into Golden Dawn activities by what it terms the “Jews of the BBC”.

Writing for Channel 4 News online, the film-maker Georgousis described his experiences while making the film:

“I was terrified that these members were proud to express their extreme ideas during campaigning openly in public. I was shocked by their hostility and by the way they treated immigrants in the Athenian squares.”

He continued: “My intentions were clear. I wanted to make an observational film to portray their hatred which haunts the streets of Athens. Sometimes I was concerned by the level of support from the Greek people.”

On Tuesday the New Democracy MP Adonis Georgiadis told Channel 4 News that the opinions expressed by Golden Dawn supporters in the documentary were not “the opinion of the majority of the Greek people.”

See the film in full below.

Warning: this video contains highly offensive and racist language