Their families shared in the struggle against apartheid and both played a prominent role in ending white minority rule in South Africa. But Thabo Mbeki, the country’s President, and Jacob Zuma, his main challenger, come from very different worlds.

The two men, both 65 and once comrades in arms, are engaged in a bitter power struggle that threatens to destroy the movement that enfranchised black South Africans and drag the country deeper into turmoil.

Mr Mbeki — bookish, with a taste for pipes, Yeats and Wordsworth — has spent the past few days ensconced in the presidential study, drafting the speech that he hopes will persuade the African National Congress (ANC) to give him a third term as party leader.

In contrast Mr Zuma, a firebrand populist given to wearing tribal dress, was doing what he does best: greeting euphoric supporters at “victory” rallies up and down the country, confident that he will unseat his great rival.

If Mr Zuma is elected as ANC president during the party’s congress, which begins tomorrow, he is almost certain to be the party’s candidate in the 2009 presidential election; a poll that the ANC is assured of winning, given its total grip on power in the country 13 years after the end of apartheid.

Mr Mbeki, whose parents were teachers and activists, is constitutionally barred from standing for a third term as President of South Africa. But he is desperate to retain control of the ANC so that he can influence the choice of his successor as the leader of the country. It is unthinkable that he would anoint Mr Zuma, whom he dismissed as ANC deputy president in 2005 after he was linked to a multibillion-pound arms scandal.

Corruption charges against Mr Zuma, the son of a domestic maid, collapsed last year on a technicality. He also beat a separate rape charge last May, which many of his supporters believe was orchestrated by pro-Mbeki supporters in an attempt to consign him to political obscurity.

At first, it seemed to have worked.Public opinion was outraged by Mr Zuma’s admission that he had unprotected sex with the 32-year-old daughter of a family friend who was HIV positive and called him “uncle”.

He later said that he took a shower to reduce the chances of infection; a statement that appalled activists in a country where 900 people a day die of Aids.

Mr Zuma fought back, capitalising on Mr Mbeki’s unpopularity, particularly among the township poor, who have seen little benefit from business-friendly, pro-market economic policies that have led to an unparalleled period of economic growth.

The President’s “denialist” stand on Aids, his refusal to criticise events in neighbouring Zimbabwe, and failure to rein in — or even admit to — one of the world’s worst crime rates, and his frequent trips abroad to further his vision of an “African renaissance” all played into his rival’s hands.

In regional conferences to decide on nominations for the five-yearly National Conference, Mr Mbeki received only 1,400 votes and the backing of four out of nine provinces.

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