Former president Jacob Zuma's corruption trial will go ahead after his special plea was dismissed.

Delivering judgment on Tuesday, KwaZulu-Natal High Court Judge Piet Koen said the former president had failed to show that State advocate Billy Downer lacked the "title" to prosecute him.

Koen said many of the allegations Zuma raised against Downer were based on speculation or suspicion or inadmissible hearsay – not on facts.

"The allegations of bias against Mr Downer were based largely on the fact that he has allegedly not been independent and objective. On a proper interpretation of [Section] 106(1)(h) of the CPA (criminal procedure act), that does not deprive Mr Downer of the title to prosecute."

Koen continued, "In the alternative and adopting a wider interpretation of the words 'title to prosecute', I am still not persuaded that Mr Downer lacks the title to prosecute or should be removed as prosecutor."

"On the evidence before me, it has not been shown that Mr Zuma's rights to a constitutionally fair trial have been impaired, or that there is a real possibility that his rights will be impaired."

The judge dismissed the matter and directed that the corruption trial should proceed.

The former president had accused Downer of turning his criminal case into "a personal legacy project of his own".

Zuma wanted Downer removed from the case, saying he did not have a "lawful title" to prosecute him.

He also said Downer lacked the independence and impartiality to conduct the case lawfully.

However, the National Prosecuting Authority (NPA) previously pointed out the courts had already conclusively found that an application for the removal of a prosecutor on the basis of bias or apprehension of bias could not be conflated with a challenge to the prosecutor's "title" to prosecute – which was often raised when non-State advocates were briefed to pursue private prosecutions.

Advocate Wim Trengove, arguing on behalf of the NPA, previously told the court that Downer "stood up for justice and truth every time and stood up to his bosses every time".

He told the court that Zuma had tried to "dress up" his fair trial complaints – which have repeatedly failed in other court cases – as a "special plea".

He added: "There is nothing new about it. There is nothing exceptional about it."

In May, Zuma pleaded not guilty to the charges against him, including corruption, fraud, racketeering and money laundering, News24 reported.

The former president faces 16 charges relating to 783 payments he allegedly received from his former financial advisor, Schabir Shaik, as well as a R500 000-a-year bribe that the State said Shaik facilitated for him from French arms company Thales.

Zuma's trial is expected to start on 11 April 2022.