Prison officers need to have stronger protection against attacks by inmates, their union has demanded after four assaults in a week.
In the latest incident, at HMP Long Lartin in Worcestershire, an officer had to be airlifted for emergency surgery after being stabbed. Three others were hurt in attacks at HMP Whitemoor in Cambridgeshire.
Mark Fairhurst, of the Prison Officers' Association (POA), said prisoners who pose the highest risk should be "totally locked down". "It's only a matter of time before one of my colleagues is murdered on duty," he added.
The Ministry of Justice (MoJ) said: "We will do whatever we can to protect our hardworking staff."
In a statement, it added: "The Lord Chancellor has announced a review into protective body armour and a trial of tasers in jails to better respond to serious incidents."
Mr Fairhurst, the POA's national chair, told BBC Breakfast: "We know our jails are awash with all kinds of illicit items, but we very rarely lock them down."
He called for facilities like so-called supermax prisons in the US, in which dangerous inmates are locked up and only have limited access to recreation and other facilities outside their cells.
