Five members of prison staff have been suspended after Woolwich murder suspect Michael Adebolajo lost two teeth when he was restrained in jail.
The 28-year-old was injured at high-security Belmarsh prison in south-east London on Wednesday, where he is being held on suspicion of murdering soldier Lee Rigby.
A Prison Service spokeswoman confirmed the incident was being investigated, adding: “Five members of prison staff have been suspended while police investigations are ongoing.”
The Prison Officers’ Association (POA) had earlier hit out at the Ministry of Justice, claiming it had done “little to avoid sensationalist reporting” of what happened.
The union said: “The POA are aware of an incident that took place on Wednesday July 17, which involved a prisoner being subjected to restraint using approved techniques called Control and Restraint.
“Our members strenuously deny any wrongdoing and the POA will be supporting them legally and emotionally during this difficult time. The use of restraint is only used where necessary when dealing with incidents up and down the country.”
It said it will fully co-operate with any police investigation, and expects the officers to be “fully exonerated”.
Adebolajo is accused together with Michael Adebowale, 22, of hacking Fusilier Rigby to death near Woolwich Barracks in south-east London on May 22. The pair are due to stand trial at the Old Bailey on November 18.
A Metropolitan Police spokesman said: “We can confirm that an allegation of assault was passed to the Metropolitan Police Service on July 17 by Belmarsh prison. An investigation has been started.”
The Prison Service again refused to comment on the detail of what is claimed to have happened.
A spokeswoman said: “The police are investing an incident that took place at HMP Belmarsh on July 17. It would be inappropriate to comment while the investigation is ongoing.”
Peter McParlin, chairman of the Prison Officers Association, accused the Ministry of Justice (MoJ) of over-reacting to the situation.
He told BBC Radio 4’s Today programme: “We have spoken to our members and on the basis of what our members have told us they have done absolutely nothing wrong.
“We are concerned that the Ministry of Justice have over-reacted due to the notoriety of this prisoner.”
Mr McParlin criticised the MoJ for failing to “correct false reporting” of the incident at Belmarsh.
He said restraint techniques were designed to minimise injuries to staff or prisoners “but sometimes there are unforeseen consequences in any violent incident”.
Mr McParlin added: “Some people have the idea that somehow it’s a sitcom like Porridge. I’m afraid the reality of the modern prison system is far different from that.”