President's question time has become one of the key items on parliament's annual calendar.

Yesterday, it provided a forum for opposition parties to get their teeth into the row around Deputy President Jacob Zuma and National Director of Public Prosecutions Bulelani Ngcuka.

Despite opposition complaints that the occasion lacks spontaneity and denies an opportunity for real engagement with President Thabo Mbeki, it is a forum opposition parties take very seriously.

Given the lack of informal contact between the president and the leader of the opposition, the Democratic Alliance's Tony Leon, it is one of the few opportunities for the opposition to engage Mbeki directly on matters of public interest.

There is usually a considerable build-up to president's question time, and the atmosphere is charged. The tension is normally broken by a round of applause from the government benches when Mbeki rises to speak.

Yesterday, for the first time, Leon was not in the house as he had left for a pre-arranged visit to London, where he addressed the Royal Commonwealth Society on Wednesday night. A Leon aide said question time had originally been scheduled for September 10 and had later been changed to September 18.

The exchanges during question time, sometimes used by Mbeki to make major announcements, can last for an hour and a half or more.

When Mbeki assumed the presidency in mid-1999, he soon faced accusations from the official opposition for not attending parliament often enough and, by implication, of not taking the institution of parliament seriously enough.

There were even suggestions that he was subtly shifting the focus of power from parliament to the expanded presidency in Pretoria.

In terms of the constitution, the president is not a member of parliament and, therefore, not under any formal obligation to attend parliament or any of its proceedings.

DA chief whip Douglas Gibson said the president's question time in the Mbeki presidency was a disappointment and a "failure".

"Questions have to be submitted long in advance. The format prevents the president from being spontaneous and it does not offer the opportunity for the opposition to really engage the president on the issues," he said.

With acknowledgements to John Battersby and The Star.