Professer Yash Pal Ghai has been fighting for a new constitution for several years

Professer Yash Pal Ghai accused the authorities of reneging on promises to bring in a new constitution.

Changing the constitution was one of President Mwai Kibaki's key campaign pledges during last year's elections.

But the coalition government is now split, especially over whether the post of prime minister should be created.

Professor Ghai told the BBC's Focus on Africa programme that he was trying to discuss the issue with Mr Kibaki but he suspected some officials were blocking that meeting.

'Big step'

"Maybe I should say to myself... these forces are larger than me and so it would be a sensible decision to step down," he said.

"It is a big step to take at this stage in the process," he said.

Raila Odinga was promised the post of prime minister

Before last December's elections, one of Mr Kibaki's key allies, Raila Odinga, was promised that he would become prime minister if the National Rainbow Coalition (Narc) defeated the then ruling Kanu party.

Narc said it would change the constitution within 100 days of forming a new government.

The constitution review commission was also rocked when one of its officials, Crispin Mbai, was murdered in September.