Boesak, who leads a three-person Congress of the People team in the Western Cape legislature, said the barrage of accusations and insults did not bode well for the dignity of political discourse in the country.

In a statement issued on Wednesday night, he cautioned both Zille's Democratic Alliance and the African National Congress that outbursts of this nature were dangerously damaging to a still fragile non-racial society.

"What South Africa and her people do not need now is political discourse conducted at the level of personal attacks rather than responsible arguments," he said.

"There is a vast and very important difference between vigorous debate and the petty viciousness that the country is now forced to endure."

He said it had to be kept in mind that Jacob Zuma had been elected president by "the vast majority" of voters through open and fair elections.

"Even if one dislikes him personally or does not agree with him politically, one must inculcate respect for the office which he holds."

The league claimed Zille was having sex with her provincial executive council, after she described Zuma as a womaniser who had put his wives at risk of contracting HIV.