A prison officer lies motionless on the floor as an inmate repeatedly kicks him in the head.
When a colleague rushes forward to help, the prisoner grabs a chair and hurls it at him before reinforcements arrive and wrestle him to the ground.
The shocking CCTV footage lays bare the brutal reality inside HMP Brinsford in Staffordshire, which was this week named the most violent prison in England and Wales by Chief Inspector of Prisons Charlie Taylor.
Behind a double layer of tall wire fences are more than 500 men, most under 25 and either serving sentences for violent crimes or on remand for serious offences including murder, robbery and rape.
A young, aggressive population riven by gang rivalries creates a tinderbox atmosphere, with more than ten assaults every week and staff struggling to maintain order.
