The brutal reality of power politics in Mugabe's Zimbabwe

In recent weeks President Robert Mugabe has gone to extraordinary lengths to tighten his grip on Zimbabwe's increasingly fractured ruling party ahead of its congress, which starts today.

Party hacks, the state media and Mugabe's wife, Grace, have publicly demeaned his vice-president, Joice Mujuru, accusing her of plotting to oust, or even assassinate, the 90-year-old president.

Last week the campaign against Mujuru - who, together with Zimbabwe's hardline justice minister, Emmerson Mnangagwa, was seen as a favourite to succeed Mugabe when he steps down or dies - was stepped up a gear.

The state-run Herald reported that Mujuru's attempt to seek re-election to the party's central committee had been derailed when her election papers - along with those of ''other Zanu-PF bigwigs linked to her nefarious activities'' - were rejected.

It also emerged that Mugabe had quietly changed the party's constitution to allow him to appoint his deputies, previously elected by the party's 10 regions.

Finally, a former war veterans' leader was arrested after accusing Mugabe of plotting "a bedroom coup" by paving the way for his wife's election to a senior Zanu-PF position.

The upshot of all this is that this week's ruling party gathering has been changed from an elective congress to a top-down meeting at which Mugabe will choose his key aides, Grace Mugabe will be appointed head of the powerful Zanu-PF Women's League, and cowed delegates will endorse all the important decisions. All that remains to be seen is whether Mnangagwa will be ''elected'' vice-president this week or at a later stage to avoid more damaging infighting.

One of Africa's longest-serving leaders, Mugabe seems determined to carry on shaping his country's trajectory long after his departure. It seems the promise of a prosperous, post-Mugabe Zimbabwe is still a long way from being realised.