British security group G4S workers have been accused of electrocuting and drugging prisoners at South Africa's Mangaung prison, the maximum security facility it ran before the government stepped in to restore order in October.

The Wits Justice Project said on Monday (October 28) some prisoners were forcibly injected with anti-psychotic medication and subjected to electric shocks.

The abuse allegations at Mangaung - the second-largest privately run prison in the world according to G4S - follow scandals at the British company such as failing to provide enough guards at the London 2012 Olympics and discrepancies in tagging prisoners in Britain.

Ruth Hopkins, an investigative journalist with the Wits Justice Project, said she had documented cases of beatings - including electro shocking - involving about 30 inmates. She had also documented about 20 cases of forced injections of anti-psychotic drugs.

"It seems to be widespread and it seems a way for the prison to control it's prison population , so they, I hear stories of how they take prisoners to single cells, they strip them naked, they pour water over over them, they put them on a metal bed frame and they electroshock them. I have not only heard this from prisoners I've heard it from wardens as well as source, an official who works for the department of correctional services and so it's widely corroborated, so video footage was leaked to me, video footage shot inside the prison and on one of the videos there is clear audio of electro shocking going on and the inmate screaming and seem to be using it as a method of interrogation," she said.

The Wits Justice Project is part of the Journalism Department of the University of Witwatersrand in Johannesburg and investigates alleged cases of mistreatment and miscarriage of justice in South Africa's prisons and justice system.

The allegations came after South Africa's Department of Correctional Services took over the facility on October 9 because the private security firm "lost effective control" of the 3,000-inmate establishment, a senior prisons official said on Monday.

James Smalberger, Chief Deputy Commissioner of Incarceration and Corrections, said safety and security issues at the prison were under scrutiny well before the most recent allegations.

Smalberger did not say his department had confirmed the mistreatment allegations made by the Wits group. The department was looking into them as part of its overall investigation into the G4S management of the prison.

Presented by Adam Justice