Jacob Zuma, the controversial leader of South Africa's ruling African National Congress (ANC), suffered a major setback today in his attempt to become the country's next president after the highest court in the country ruled that documents seized in police raids could be used in evidence at his forthcoming trial on corruption and racketeering charges.

Nine out of 10 judges of the Constitutional Court upheld an earlier Supreme Court ruling that warrants used in raids on the offices and homes of Mr Zuma and his lawyers were valid.

The ruling opens the way for the state to present nearly all the evidence it has amassed against the former vice-president in five years of investigation which has split the ruling party and led to the country's biggest political crisis since the end of apartheid in 1994. The ANC has voted to disband the police unit that headed the investigation, which is known as the Scorpions.

Mr Zuma, 66, who is nevertheless still the favourite to take over as the country's president after elections next year, faces 16 charges including money-laundering and racketeering in a case which also implicated the French arms firm Thales. Mr Zuma denies any wrongdoing.

"All the applicants' challenges to the search and seizure operations failed," Chief Justice Pius Langa found in a majority judgment.

The judge said the court found "nothing untoward" in a raid conducted by the Scorpions, South Africa's crack crime-fighting unit, on the home of Mr Zuma in August 2005. Mr Zuma, who frequently says he wants his day in court but has appealed time and again to delay the hearing, was ordered to pay costs.

President Mbeki fired his then deputy president in 2005 after Mr Zuma's financial adviser and close ally was found guilty of corruption and fraud. The move triggered a bitter power struggle which resulted in the charismatic and popular Mr Zuma capturing the ANC presidency from Mr Mbeki last December.

By so doing, he virtually guaranteed he would be the ANC's candidate in elections in April and, given the party's political dominance, is almost certain to become South Africa's third black president.

Many South Africans, including Archbishop Desmond Tutu, say Mr Zuma, who was acquitted on rape charges in May 2006, is unfit to follow in the footsteps of the anti-apartheid icon Nelson Mandela.

ANC loyalists, however, say Mr Zuma, who served 10 years on Robben Island and is deeply popular among the grassroots, is a victim of a plot by the aloof and bookish Mr Mbeki and his close associates.

Since Mr Zuma took the ANC leadership, the party has piled pressure on all his critics, including the judiciary and it plans a huge demonstration when the corruption trial formally starts next Monday. Mr Zuma has said he will step down as ANC president only if found guilty, but he has gone out of his way to prevent a trial starting before the presidential elections, by which time it is expected he would have immunity.

In a swift reaction to the ruling, the ANC said it respected the decision of the court but expressed doubts that its leader would get a fair trial.

It said the manner in which his case has been handled by the authorities "reinforced the perception that the ANC president is being persecuted rather than merely prosecuted."

"It has also fuelled doubts about his chances of receiving a fair hearing,” it said.

ANC leaders and supporters plan to stage a huge show of force outside the Pietermaritzburg High Court on Monday to show their support, even though both prosecution and defence lawyers have agreed they are not yet ready for the case to go forward.

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