The African National Congress (ANC) says it is standing behind secretary general Ace Magashule in the face of an "ongoing vilification campaign" to tarnish his image.

This follows a City Press report which indicated that a British investigative NGO had apparently found "damning evidence" of corruption in the Free State when Magashule was premier and that it was willing to testify before the State capture commission of inquiry.

The NGO, Shadow World Investigations, formerly known as Corruption Watch UK, reportedly found evidence that the Gupta family sold computers worth R1.7-million to the provincial government for more than double their worth.

It also claimed that former agriculture MEC Mosebenzi Zwane, allegedly received benefits from Gupta companies after signing a 90-year lease with the Guptas for the Estina farm.

ANC spokesperson Pule Mabe said the NGO was rehashing old allegations that had never been substantiated and that Magashule should not "dignify these insults with a response".

"The ANC does not see these allegations in isolation, but as part of a well-orchestrated and co-ordinated vilification campaign against our secretary general and to further fuel divisions," he said.

"It is not clear why this NGO would devote so much resources and energy toward pursuing narrow political agendas by seeking to tarnish the image of some leaders. The question arises: Whose agenda are they serving?"

Mabe said they were committed to freedom of expression and the free flow of information. However, they did not believe that "malicious campaigns" advanced the cause of freedom of expression and nation-building.

"We call on all leaders and members of the ANC to unite and expose these divisive tendencies from whatever quarter they may be coming from. Our unity and renewal project demands that we all stay vigilant against wedge-drivers."