Former premier Dr Mahathir Mohamad continues to fire salvos at his protege turned nemesis in a series of interviews with the foreign media.

In his latest interview with The Telegraph , the 90-year-old statesman related how the police came knocking when he criticised attorney-general Mohamed Apandi Ali.

"The police came here to my office, but I refused to answer their questions.

"I told them that if they wanted to question me, they should do it in court, where everyone can hear what I have to say and my lawyers can question them," he was quoted as saying.

According to the UK daily, Mahathir smiled and shook his head when asked if he was concerned about being hauled to court.

"If I'm made to appear in court, I'll be happy to answer. They are trying to rule by intimidation, but I am ready for it," he said.

Mahathir also regurgitated his allegations against Najib, claiming that various quarters had come to him seeking help because the prime minister was "destroying" Malaysia.

"We have laws to deal with corruption, but our prime minister is undermining rule of law. He can't be allowed to get away with this. If you question him, if you go to the police, you could end up being detained and charged yourself.

"If these allegations aren't true, why doesn't Najib sue? He denies them, but chooses not to sue. And instead his new attorney general wants to jail government whistle-blowers for life. That is how they deal with these allegations," he said.

The former premier also expressed disappointment with Najib.

"I expected more. He has let us all down. We cannot let this continue," he said.

The Telegraph said Mahathir also focused on the "lavish lifestyle" of Najib's wife Rosmah Mansor and raised questions about the family's ties to financier Jho Low.

He also acknowledged that as long as Najib and his allies dominated the domestic political landscape, it was unlikely that investigations in Malaysia would bring him down.

However, he said investigations being carried out abroad with regard to 1MDB could change the equation.

"These foreign inquiries are more likely to determine what happens here," he said.

Najib has repeatedly denied using public funds for personal gain and blamed Mahathir and others of conspiring against him.