Austria's former vice-chancellor and longtime leader of the far-right Freedom Party pleaded not guilty in his trial for alleged corruption on Tuesday, in a case stemming from a scandal that brought down the government.

Heinz-Christian Strache, one of Europe's most high-profile far-right leaders, was forced to resign as vice-chancellor in 2019 after a video was published showing him offering public contracts in return for electoral campaign support from a woman posing as a Russian investor.

The scandal, dubbed "Ibiza-gate" because the video was secretly filmed on the Spanish party island, spawned a sweeping corruption investigation that uncovered several different accusations of wrongdoing.

A prosecutor laid out the charges in the current trial on Tuesday, saying Strache stood accused of a "serious crime" that was "no trivial offence".

The trial concerns charges that Heinz-Christian Strache helped to change a law for an FPOe donor when he was in a coalition government
The trial concerns charges that Heinz-Christian Strache helped to change a law for an FPOe donor when he was in a coalition government AFP / ALEX HALADA

Strache arrived at the court in Vienna wearing a face mask and a dark suit, refusing to comment to journalists.

The 52-year-old took copious notes as the prosecutor spoke, before taking to the stand himself in the afternoon, answering questions politely but at times defensively.

Austria's former far-right leader Heinz-Christian Strache was forced to resign as vice-chancellor in 2019 over the "Ibiza-gate" scandal
Austria's former far-right leader Heinz-Christian Strache was forced to resign as vice-chancellor in 2019 over the "Ibiza-gate" scandal AFP / ALEX HALADA

The trial concerns charges that Strache helped change a law for a Freedom Party (FPOe) donor when he was in a coalition government with the centre-right People's Party (OeVP) of Chancellor Sebastian Kurz.

The donor, Walter Grubmueller, had invested in a private clinic in Vienna.

He is a long-standing friend of Strache's and told a parliamentary committee that he had invited Strache aboard his yacht and on a vacation at his holiday home on the Greek island of Corfu in 2016.

While negotiating the coalition agreement with the OeVP, Strache directly asked the clinic owner "which amendment to the law" he would need for his "clinic to finally be treated in a fair manner", according to chat messages uncovered in the investigation, which were leaked to the media.

Austrian Chancellor Sebastian Kurz has also been dragged into the scandal
Austrian Chancellor Sebastian Kurz has also been dragged into the scandal AFP / ALEX HALADA

In the messages, the donor reportedly said that he would deliver a draft law to the FPOe's party headquarters.

After Strache took office in 2017, the far-right took charge of the health ministry and went on to oversee a change in the law that widened the category of establishments eligible for public funding.

According to expert estimates, this meant clinics like Grubmueller's were allowed to apply for as much as 2.2 million euros ($2.6 million) in funding in 2019 alone.

Grubmueller, who is standing trial alongside Strache, also pleaded not guilty, describing the charges against him as "laughable".

The trial concerns charges that Heinz-Christian Strache helped to change a law for an FPOe donor when he was in a coalition government
The trial concerns charges that Heinz-Christian Strache helped to change a law for an FPOe donor when he was in a coalition government AFP / ALEX HALADA

Strache's lawyer Johann Pauer insisted that his client had not "gained any advantage while he held office" from his dealings with Grubmueller.

Strache had not been aware when the law was changed that Grubmueller would later make a donation of 10,000 euros to the party, Pauer added.

Strache himself in his testimony denied having raised the issue of funding for such clinics in the coalition talks.

The reforms to private healthcare funding was "about the principle of fighting unfair treatment" of establishments such as Grubmueller's, Strache insisted.

He added that this Grubmueller's donation was "insignificant" for the party, which Strache said "was never dependent on donations".

When the "Ibiza-gate" footage emerged in 2019, the coalition between the Freedom Party and the People's Party collapsed.

In the video, Strache claimed that several high-profile billionaires and international gambling company Novomatic had been funding political parties through off-the-books donations to associations, some owned by high-ranking OeVP politicians.

All those named by Strache deny any wrongdoing.

The claims triggered an array of investigations, including a probe into the appointment of Thomas Schmid -- a civil servant and Kurz ally -- as head of the Austrian state holding company OeBAG.

Since Strache resigned after 14 years at the helm of the Freedom Party, he has also been accused of embezzling party funds to pay for his luxurious lifestyle.

The revelations disillusioned many of the party's voters, and the FPOe slumped from 26 percent of the vote in the 2017 general election to 16 percent in 2019.

The FPOe has spent much of the time since the scandal consumed by infighting.

Last month Strache's successor as leader, Norbert Hofer, resigned after weeks of tension with party colleague and former interior minister Herbert Kickl.

Kickl, seen as a party ideologue and mastermind of some of its anti-Islam and anti-migrant campaigns, took over as leader.