Veteran advocate George Bizos says politicians facing criminal cases must not scandalise the National Prosecuting Authority and the Scorpions, as this would undermine the constitution and democracy.

Although Bizos did not mention any names to delegates at a national conference to assess the performance of the Scorpions yesterday, ANC deputy president Jacob Zuma and former Limpopo premier Ngoako Ramatlhodi had in the past questioned the political motive of the NPA.

Zuma was charged with corruption but the charges were subsequently withdrawn - the NPA wants to reinstitute them - while Ramatlhodi is being investigated, and was raided on suspicion of corruption.

Both politicians have accused the NPA of being politically manipulated to convict them as part of the succession battle in the ANC.

Zuma's supporters in the ANC Youth League, Cosatu and the Young Communist League had hurled insults at former national director of public prosecutions Bulelani Ngcuka and, of late, some invective has been directed at the current prosecutions boss, Vusi Pikoli.

But Bizos said that as much as there was nothing wrong with criticising these institutions, scandalising them was undermining the legitimacy of the country's criminal justice system.

"The NPA and the Scorpions are often accused of improper conduct by those whom it has decided to prosecute, who proclaim that they have been persecuted and that they are innocent.

"Those convicted claim that their trials were unfair even if they have been found guilty by higher courts of appeal not to have been so."

Zuma's former financial adviser, Schabir Shaik, and former ANC chief whip Tony Yengeni - both convicted on separate cases - claimed they were treated unfairly.

Former ANC activist and cleric Allan Boesak - who was convicted of fraud, served his sentence but was later granted a presidential pardoned - also protested his innocence.

Bizos said people with high political profiles were reluctant to accept the impartiality of prosecutors.

"We are all free to criticise the courts and the prosecutors, but scandalising them undermines our constitution and democracy."

With acknowledgements to Moshoeshoe Monare and The Star.