For the first time in his protracted political career, former premier Dr Mahathir Mohamad set foot in Parliament House as the chairperson of an opposition party.

Mahathir, who was prime minister for 22 years, arrived at the building to attend a special meeting on parliamentary privileges and immunity of MPs.

Also in attendance were Parti Pribumi Bersatu Malaysia (Bersatu) president Muhyiddin Yassin, Parti Warisan Sabah president Shafie Apdal, PKR president Dr Wan Azizah Wan Ismail and DAP parliamentary leader Lim Kit Siang.

More than 30 opposition lawmakers were present for the meeting held at a temporary building in the Parliament complex.

However, former second finance minister Ahmad Husni Hanadzlah was not seen, while for PAS, only Pokok Sena MP Mahfuz Omar attended.

Mahathir during the meeting was seated next to opposition leader Dr Wan Azizah Wan Ismail - the wife of his former nemesis Anwar Ibrahim.

In his opening remarks, Mahathir spoke of the three former ministers - Muhyiddin, Husni, and Shafie - who are now under police investigation for their speeches in the Dewan Rakyat, which touched on 1MDB.

He said the freedom of the three had been curtailed and they joined the ranks of ordinary people and Umno members who are not allowed to speak on 1MDB and the RM2.6 billion donation to Prime Minister Najib Abdul Razak.

"I don't think they (the former ministers) are saying anything that is not already common knowledge. Now, they are accused of exposing government secrets.

"The Official Secrets Act has to do with (protecting) government policies, not protecing crimes committed while in government," said Mahathir, who added it was the duty of those with knowledge of a crime to report it.

"But now they can't. They will be questioned by the police and charged in court, on baseless charges," he said.