The protest was led by Peter Magyar, a former government insider who plans to challenge Prime Minister Viktor Orban’s Fidesz party.

The protest on Saturday was led by Peter Magyar, 43, a former government insider turned critic who used to be married to Orban’s ex-justice minister Judit Varga.

Magyar has said he also plans to challenge Orban’s Fidesz party by eventually launching his own, pro-European Union political party.

On Saturday, reports said more than 10,000 people were expected to join the demonstration.

Protesters marched towards Hungary’s parliament some of them shouting, “We are not scared” and “Orban resign!”

Many wore the red-white-green national colours or carried the national flag, symbols that Orban’s party used as their own for the past two decades.

“These are the national colours of Hungary, not the government’s,” 24-year-old Lejla, who travelled to Budapest from Sopron, a town on the country’s western border, told the Reuters news agency.

Magyar became widely known in February when he became the government’s whistleblower and delivered incendiary comments about the inner workings of Orban’s administration.

In March, he published a recording on his Facebook page of a January 2023 conversation with his ex-wife Varga, in which she detailed an attempt by aides to Orban’s cabinet chief, Antal Rogan, to interfere in the prosecution files in a corruption case centred on former Ministry of Justice State Secretary Pal Volner.

“They suggested to the prosecutors what should be removed,” Varga says in the recording.

Magyar said the tape proves top officials in Orban’s government are corrupt, and that he had given the recording to the Metropolitan Public Prosecutor’s Office in Budapest, to be used as evidence.

The office has said it would analyse the tape and further evidence would be collected.

Orban under pressure

This probe has come at a politically sensitive time for Orban in advance of European parliamentary elections in June.

It also follows a sex abuse scandal that brought down two of his key political allies – the former president and Varga – in February.

According to data by pollster Median, published by news weekly HVG in mid-March, 68 percent of voters have heard of Magyar’s entry into the political field and 13 percent of those said that they were likely to support his party.

On Saturday, some protesters also said Magyar appealed to them because he had been close to the Orban government and has an inside knowledge of how it works.

“We had known that there is corruption, but he says it as an insider and confirmed it for us,” Zsuzsanna Szigeti, a 46-year-old healthcare worker wearing a Hungarian flag that covered her entire body, told Reuters.

She added that she was concerned about the education and the healthcare systems, and worried about corruption.

“I trust that there will be a change,” she said.