The royalty should not comment about politics but Prime Minister Najib Abdul Razak's management of 1MDB appears to have even irritated the Johor crown prince, said Dr Mahathir Mohamad.

"He should not be making any comment on politics but sometimes when things are irritating, you have to scratch a bit," he told a press conference in Kuala Lumpur today.

He was asked to respond to Tunku Ismail Sultan Ibrahim who criticised Najib as someone who "had everything to hide" when the prime minister failed to turn up at a dialogue on 1MDB titled "Nothing to Hide".

Mahathir was also present at the dialogue.

Najib had said the dialogue had turned into a debate format and it would not have been appropriate for him to debate Mahathir openly.

However, Mahathir today said he had no intention of debating Najib at the dialogue.

He also sarcastically said it was his "mistake" that the prime minister was under such an impression.

"Oh yes, that was my mistake. I thought it was an open debate, people said I was going to attend.

"But I didn't want to debate, I just wanted to ask questions like everyone else. All the NGOs were there, I was also an NGO," he said.

On a separate matter, Mahathir disagreed with Johor Sultan Ibrahim Ismail Iskandar's call for English schools to be implemented in the country.

He concurred with Deputy Prime Minister Muhyiddin Yassin that it would be against the National Education Act 1996.

However, Mahathir said the way around this would be to reintroduce the teaching of mathematics and science in English and make English language a compulsory pass subject.

The policy was introduced under Mahathir's leadership but was scrapped after Najib came into power.