In the most significant political upheaval since the ANC won power with the collapse of apartheid in 1994, Mr Zuma has assembled a seemingly unassailable coalition from the party’s left wing and factions opposed to Mr Mbeki in a bitter and sometimes dirty leadership race that has divided the party and  country. Mbeki had fought hard to retain control of the ANC,  even after his constitutional obligation to step down as South Africa’s President in 2009. But support for him has dwindled in recent weeks as his authoritarian style, market-oriented economic policies and controversial positions on Aids and Zimbabwe have taken their toll.

But Zuma, 60, cannot count on succeeding Mbeki even though normally the ANC leader would be a near certainty to be the party’s presidential candidate and win the general election.

South African prosecutors are deciding whether to charge Zuma with corruption over a £4bn weapons deal. His financial adviser, Schabir Shaik, is serving a 15-year jail sentence for facilitating bribes to Zuma from an arms company. Mbeki sacked Zuma as deputy president when they came to light.

Some have accused Zuma of seeking the presidency in order to forestall a prosecution. The accusation has been given weight by talk within the Zuma campaign of trying to push Mbeki from office and engineer an early general election.

That would take a vote in parliament and it is unclear whether Zuma could muster support from a majority of ANC MPs to do so. If not, power would be divided between Mbeki as president and Zuma as ANC leader for the next 18 months - extending the struggle that has split the party more than at any time since 1994.
The contest has grown increasingly bitter and controversial, with both camps accusing the other of buying votes with job offers and cash.

Mbeki has attacked Zuma as unfit for office owing to the corruption allegations and a trial for rape. Zuma was acquitted, but drew widespread criticism when he admitted to unprotected sex with a young family friend he knew was HIV-positive. Zuma said he took a shower instead of using a condom, which angered Aids campaigners because he was at the time head of the country’s National Aids Council.

Last week, Mbeki said he approved of a statement by Desmond Tutu in which the former archbishop of Cape Town said that the ANC “must not elect someone the country will be ashamed of.”

Zuma responded by attacking Mbeki for centralising power and exercising undue influence over the judiciary and parliament and criticised the vast wealth gap that continues to exist in South Africa.

In a speech this week, Zuma took a dig at Mbeki’s Zimbabwe policy, saying, “When history eventually deals with the dictators, those who stood by and watched the deterioration of nations should bear the consequences.”
Mbeki told The Mail and Guardian newspapers in Johannesburg that he had never known such acrimony within the ANC. He rejected charges that people within the party were afraid of him.

“Do I look as if I've got horns? Its said that I block and inhibit open discussion. That’s puzzling to me, it's completely untrue,” said the president.

Zuma has received about 60 per cent of the nominations from the ANC’s branches, which will decide the race. He has also won the backing of the unions, the party's women’s and youth leagues and Mosima Gabriel, a billionaire businessman who pulled out of the race and brought his supporters to Zuma’s camp.

Zuma, a populist who has at times declared himself a socialist, has been working hard to shore up the confidence of businessmen at home and abroad who fear that his populist rhetoric and backing from the unions and the Communist party will lead to a shift away from Mbeki's market-oriented economic policies.