Counter-terrorist units are investigating an attack on two prison officers at Full Sutton maximum security jail near York.
One warder was held hostage for several hours by three inmates.
The Prison Service has stressed that they were not serving sentences for terror-related offences.
The attack comes less than a week after the murder of Drummer Lee Rigby in Woolwich.
Gregg Easteal reports.
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Sandiford, a former legal secretary originally from Redcar, was convicted of drug smuggling offences and sentenced to death in 2013.
Durham Crown Court heard that one of the male victims suffered a triple-fractured jaw, while left lying in the gutter, unconscious.