Prison officials are investigating after shocking footage of an assault on an inmate was leaked online.
Inmates filmed a brutal assault on a fellow prisoner, in which the victim is grabbed around the neck and repeatedly slapped in the face and brought to tears.
The distressing footage, filmed in a cell at Brixton prison, has been viewed over 200,000 times.
It is believed to have been filmed earlier this month on a mobile phone smuggled into the prison.
In shocking scenes, the young prisoner is held on the ground by his throat while he is assaulted before being hauled into a chair.
At one point the clearly distressed prisoner is told: "You know where you are? You're in Brixton you know."
Since it first appeared on Instagram, the video has been taken down and an investigation launched.
But a new posting on Facebook this week has racked up thousands of views.
A spokesman for the Prison Service said: "This behaviour is totally unacceptable.
"We have identified those involved and they have been stripped of their privileges and will be moved to other establishments as punishment. We have also referred this incident to the police for investigation.
“As the Prime Minister and Justice Secretary have said, our prisons are in need of reform.
"That is why we are investing £1.3 billion to transform the prison estate over the next five years, to better support rehabilitation and tackle bullying, violence and drugs."
It is a criminal offence to bring mobile phones into prison and the Prison Service is working to introduce signal blocking technology at its institutions.
