A deputy prime minister's ascension to the post of prime minister is only tradition, not law, says former prime minister Dr Mahathir Mohamad.

"(Abdullah Ahmad Badawi) resigned in 2009 and Najib Abdul Razak, as the deputy prime minister, took over.

"This is by tradition, not because of any particular rule or law," Mahathir said in his blog today.

This posting on succession as head of the country’s government comes as Mahathir continues his efforts to get Najib out of office.

The succession tradition is in question today, as Najib's current deputy, Ahmad Zahid Hamidi, is an Umno vice-president.

This means that if Najib steps down, there is a chance that suspended Umno deputy president Muhyiddin Yassin, who is Mahathir's ally, could seize the party's top post to become the new prime minister.

Mahathir and Muhyiddin are part of the Save Malaysia group, which also includes opposition and civil society leaders.

The group aims to oust Najib through legal means, and implement institutional reforms.

However one of the group’s leaders, DAP supremo Lim Kit Siang, has said that they have not yet worked out who should succeed Najib if their plan works.