A former Polish deputy justice minister was detained by the Internal Security Agency on Monday, his lawyer said, after he lost parliamentary immunity as part of a probe into the misuse of public money for purposes including political campaigning.

Prosecutors allege that members of the arch-conservative Sovereign Poland party, a junior partner in the nationalist Law and Justice (PiS) government that left office in December, misused money from the Justice Fund, which is intended to help victims of crime.

During its eight years in power, PiS was accused by critics at home and abroad of undermining democratic rules, turning public media into a government mouthpiece, and reshaping the country according to its deeply conservative values.

Prosecutors say they have evidence that former deputy justice minister Marcin Romanowski committed 11 crimes including exceeding his powers and causing the state treasury to suffer losses. A spokesperson said he would be brought to the National Prosecutor's Office to be charged and questioned as a suspect.

Romanowski denies the accusations and has said that moves to have him arrested are politically motivated.

Local media have reported that money from the fund was used to curry favour with rural voters in seats targeted by Sovereign Poland by buying everything from fire engines to equipment for country housewives' associations.

Prosecutors have also said that 25 million zlotys ($6.41 million) from the fund was used to buy Pegasus phone-hacking software.

Sovereign Poland lawmaker Michal Wos on Friday also lost his parliamentary immunity and is accused by prosecutors of misusing money from the Justice Fund to buy Pegasus. He denies any wrongdoing and has said that Pegausus was used to fight crime.

The pro-European coalition government of Donald Tusk says it has opened the way for prosecutors to investigate wrongdoing under the previous administration that would previously have been covered up.

Justice Minister Adam Bodnar said on Monday it was possible further charges could be pressed against other figures linked to the previous government, but that no decision had been taken yet.