South African authorities are predicting a record turnout for tomorrow's general election, widely seen as the most important since the end of apartheid.

There are more than 23 million registered voters in the country of 50 million people, and the Independent Electoral Commission predicts that 80 per cent of them will cast their ballot. "We are expecting the largest voter turnout because a large number of people have shown interest in these elections," said the IEC's Brigalia Bam.

The result is not in doubt. The ANC leader Jacob Zuma will be the next president of South Africa. However today's ballot is the first major electoral test for the ruling African National Congress whose two-thirds majority is under threat from a breakaway party, Cope; the Democratic Alliance and a host of smaller parties. Mr Zuma was being typically bullish ahead of voting. "We expect that the people of this country will once again give the ANC a huge and decisive mandate," he told reporters yesterday.

Pictures of the extraordinary scenes that characterised South Africa's first democratic election in 1994 still adorn walls all over the country. The snaking queues of thousands of people who had been prevented from voting under apartheid are likely to be repeated this year although the weeks-long wait for results has been reduced, with official figures expected from Saturday.

Serious competition at the polls has drawn an expensive response from the ANC, which has spent an estimated £34m in a campaign which has sought to emphasise the power and popularity of the party. The party of Nelson Mandela, who although frail has been wheeled out for two election appearances, currently has 297 MPs in the 400-seat parliament. The scale of the party's victory will decide how bold any possible changes will be from a new president who is viewed with considerable unease by many. Markets in Africa's biggest economies reflected increased fears that Mr Zuma, who comes from the left wing of the party, may achieve a two-thirds mandate which would allow him to make changes to the constitution.

The contradictory pressures on the unpredictable president-in-waiting are reflected by his relationship with two key party figures: the country's influential Finance Minister Trevor Manuel and the controversial ex-wife of Nelson Mandela, Winnie Madizekela Mandela.

The former is a fiscal conservative whose popularity with business leaders means he must be retained and the latter is a fiery populist with strong Communist party backing. Mr Zuma is expected to find room for both of them in his post-election cabinet.

Senior figures from the business world have sought and received reassurances that Mr Manuel will remain in his post. Reports that he was set to resign after the departure of the former president Thabo Mbeki last year were enough to send markets and the rand into a steep decline.

"The one thing I know, and I have worked with Jacob Zuma for almost two decades, the one thing I know is that he will draw on highly skilled individuals," the Finance Minister said yesterday. "He wants to succeed. He is not going to set himself up for failure."

However, Mr Zuma is expected to make some populist appointments with party sources mentioning Winnie Mandela for a possible senior post. The 72-year-old has spent much of the past decade in the political wilderness after convictions for theft and fraud while head of the ANC Women's League. She was earlier found guilty of kidnapping and held to be an accessory to the killing of a 14-year-old boy, Stompie Seipei, who was targeted by her own vigilante bodyguard, the Mandela United Football Club.

Despite these convictions and a past sacking for incompetence she remains extremely popular in the poorer townships and she still lives in the Orlando East area of Soweto.