Constitutional experts have warned that the adverserial nature of politics around the Hefer Commission and corruption investigations against senior politicians could undermine the constitution.

They have particularly raised alarm about Deputy President Jacob Zuma's latest attack on Bulelani Ngcuka, the national director of public prosecutions, saying Zuma might have overstepped the line.

Eminent law professors argued that his attack could be seen as an infringement of Ngcuka's office, a constitutionally protected institution of which the independence is guaranteed.

Zuma said last week that he had referred his complaint that Ngcuka had misused his office, in the way he conducted an investigation into him, to the public protector. He claimed that correspondence with the French company that he was alleged to have solicited a bribe from had "cleared" him of wrongdoing.

This obtaining of information from a company still being investigated, the lawyers believe, could also be seen as an interference in terms of the National Prosecutions Authority act into an investigation. The Scorpions probe into Zuma's financial adviser, Schabir Shaik, is at a stage of sensitive negotiations with the French judiciary to have a second investigation done into the company, Thales, an arms deal beneficiary.

But in parliament last week, Justice Minister Penuell Maduna rejected suggestions that the Scorpions investigation into the deputy president was ever interfered with. "I must say there was never any attempt at political manipulation," Maduna said. "I have never been told by anyone that the deputy president, or for that matter any person, acted in contravention of this section (of the Act)."

Lawyers disagree. Pierre de Vos, constitutional expert from the University of the Western Cape, argued that Zuma might have gone too far.

"Of course these issues are difficult to pin down in law and whether it would constitute a contravention of the NPA Act is complicated", De Vos said. "But as a matter of general principle, it is very untoward for a person so high up in the executive to so directly... attack a body (of which the independence is protected in the constitution)."

Gerhard Erasmus of the University of Stellenbosch said politicians needed to be more circumspect in times of crisis, because the impact of their actions would not be limited to the current saga. "If one thing is required now of politicians, it is to give guidance with respect to integrity and respect for the constitution," said Erasmus.

Zuma's office pointed out that he made it clear in the statement "that he has never questioned the right of the NDPP to investigate him should he believe there was reason to do so".

"What he questioned was why the investigation was continued after the French said there had been no solicitation of a bribe," Zuma's spokesperson, Lakela Kaunda, said.

With acknowledgements to Christelle Terreblanche and The Mercury.