Fraudster and former African National Congress chief whip Tony Yengeni is digging his own grave by attacking members of the National Prosecuting Authority (NPA) - and might face a civil suit.

According to a senior NPA official, Yengeni has angered top brass in the NPA, including those who might have seen his four-year jail term for defrauding parliament as a bit harsh.

"But now he is attacking our staff members, calling them racists and rubbishing the prosecuting authority. This guy is shooting himself in the foot," said the source.

In a second affidavit in support of his Pretoria High Court bid to have his conviction and sentence overturned, lodged with the court on Thursday, Yengeni rounded on former national director of public prosecutions Bulelani Ngcuka.

He accused him of being an "agent in the hands of the most backward, reactionary rightwing political forces in the country".

Yengeni claimed Ngcuka had led a vendetta against him as he (Yengeni) had become aware during the 1980s, when he was Western Cape leader of Umkhonto weSizwe, that Ngcuka was suspected of being an apartheid government spy.

Ngcuka last year weathered allegations that he had been Agent RS452, which led to the Hefer Commission of Inquiry.

A former Eastern Cape human rights lawyer, Vanessa Brereton, subsequently admitted she had been RS452, and the commission found there was insufficient evidence to conclude Ngcuka had been a spy.

"These spy allegations against Ngcuka are thus not new and were made against him in the 1980s. Ngcuka knows of my knowledge of his activities and this strengthens his vendetta against me," Yengeni alleges in the new affidavit.

He claims further that Ngcuka worked with rightwing political forces, pointing to the fact that Ngcuka had appointed advocate Jan van Vuuren - who had prosecuted Yengeni for treason in the late 1980s - to lead the prosecution in the parliamentary travel voucher scam case.

The source said the NPA was concerned about "Yengeni tarnishing the names of our professionals".

"These guys are doing their professional job - they don't have time for personal vendettas. They interpret and apply our laws professionally."

"What kind of criminal justice system are we running and what kind of message will we be sending when we have to throw all white prosecutors away, or switch them for (black prosecutors) when a black politician is involved in a criminal case?" the source asked.

He said Yengeni's move was a last-ditch effort to save himself from going to jail.

Glenn Penfold, a lawyer with the firm Webber Wentzel Bowens, said that because Yengeni had made the allegations against Ngcuka in an affidavit before court, he was protected by qualified privilege.

"However, Ngcuka could still sue Yengeni if he can prove that Yengeni acted out of malice."

"In other words, Ngcuka would have to prove that Yengeni was motivated by spite, ill-will or improper motive."

Had Yengeni made the allegations out of court, Penfold added, a court would regard the statements as defamatory and the onus would be on Yengeni to prove their truth.

Ngcuka's spokesperson, Sipho Ngwema, said they had not taken a position on how to respond to Yengeni's allegations.

"We might want to leave it like that or take it to a court of law. But we have not decided at this stage," said Ngwema.

Makhosini Nkosi, spokesperson for the NPA, said: "We will do all our talking in court."

With acknowledgements to Moshoeshoe Monare, Lee Rondganger and The Star.