The security firm Serco has promised a safety review after a female prison officer was left fighting for her life following an attack at a crown court.
The woman - believed to be in her 50s - remains in a critical condition in hospital after she was seriously assaulted by a male prisoner at Blackfriars Crown Court in London, Scotland Yard said.
A 22-year-old man has been arrested on suspicion of attempted murder and remains in custody at a south London police station.
Kevin Hagan, Serco's contract director, said: "One of our employees is in a critical condition after she was seriously assaulted yesterday by a male prisoner at Blackfriars Crown Court. Our thoughts are with her and her family at this time.
"We take a zero tolerance approach to violence against staff and we always press for the most serious charge to be laid against those responsible."
A spokesman for Serco said the prisoner custody officer was not left alone with her attacker and had been working alongside colleagues at the time.
Asked whether safety procedures were being reviewed in light of the attack, the spokesman replied: "There will be a review inevitably."
Detectives from Scotland Yard's Homicide and Major Crime Command are investigating the incident.
The woman was attacked at around 1.35pm yesterday as she escorted the prisoner between the court and a waiting van which was parked inside the court yard.
London's Air Ambulance was called and the victim was treated at the scene before being taken to an east London hospital.
Anyone with information that could assist the investigation is asked to call the incident room based at Sutton on 020 8721 4054, or Crimestoppers anonymously on 0800 555 111.