Jacob Zuma, the man most likely to be South Africa’s next president, delivered a strong warning to the country’s judges today against jailing him on corruption charges, as his supporters predicted blood in the streets if the ANC head was convicted.

In a high-energy impromptu rally on the steps of the Johannesburg courthouse, the president of the ruling African National Congress party vowed that if he was sent to prison he would not go alone. In Zulu, he declared that if there was a criminal trial, he would “call witnesses”, in an apparent reference to his bitter political rival, President Thabo Mbeki.

The 66-year-old former guerrilla leader broke into a dance as he led thousands of roaring supporters in a rendition of Bring Me my Machinegun, the anti-apartheid song that has become his trademark.

The threat followed a judge’s announcement that he would rule on September 12 whether to dismiss fraud and corruption charges against Mr Zuma, who stands accused of accepting bribes from a French arms company in a multibillion-dollar arms deal in 1999.

Mr Zuma, who was dismissed by Mr Mbeki in 2005 over the scandal, has long hinted that the President himself was involved, a suggestion he has tried to use as leverage to avoid his own prosecution. He claims that the lawsuit is part of a political conspiracy aimed at thwarting his presidential ambitions.

He is already campaigning for elections that must be held by mid-2009, and the South African Constitution bars anyone from running for office if they have been sentenced to more than 12 months in prison.

The Johannesburg Sunday Times last weekend quoted a secret report that Mr Mbeki accepted 30 million rand (£2.9 million) from a German arms company and gave 2 million rand to Mr Zuma and the rest to the ANC. The President’s office has dismissed the report as nonsense.

“The truth will be revealed,” Zuma said, to chants of “30 million! 30 million!” from the crowd.

“Our president is the target of a political conspiracy and we are convinced that the conspiracy is led by the state President [Mr Mbeki],” Julius Malema, the head of the influential ANC Youth League, told the rally.

To loud cheers, Mr Malema warned the country’s judges to keep their hands off Mr Zuma and demanded that Mr Mbeki stand down immediately to make way for his presumed successor.

“If you touch the old man, you must touch us first. Nobody will arrest Zuma as long as we are alive,” Mr Malema said. “Before you get to him you must kill the youth of this country. We are prepared to die for Zuma.”

One of the most colourful political figures on the African continent, Mr Zuma has long been under a cloud because of the 1999 French arms deal, but a chief prosecutor decided not to press charges in 2003. New charges were filed against Mr Zuma in 2005, but these were thrown out in 2006 on a technicality.

In 2006 he was acquitted of the rape of an HIV-positive family friend, but not before attracting widespread criticism from health experts for testifying that he showered after sex to reduce his chances of infection.

Days after he was elected as ANC president last year, the National Prosecuting Authority said that it had new evidence, and filed racketeering, corruption, money laundering and fraud charges against Mr Zuma in respect of the 1999 arms deal.

His election further deepened the rift in the ANC between his supporters and those of Mr Mbeki. Today, dozens of the ANC’s top brass accompanied Mr Zuma to court in a show of solidarity.

Judge Chris Nicholson said if he didn’t throw out the case, then Dec. 8 would be the provisional starting date for Mr Zuma’s trial.

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