UPDATE: Milton Keynes Oakhill '˜youth prison' officer in coma following alleged attack by inmates

The man, who is only 21, has been airlifted to John Radcliffe hospital at Oxford with critical head injuries.

It is understood that five youths, aged 14 and 16, have been arrested by police on suspicion of attempted murder.

The alleged attack is believed to have taken place on the unit’s football field at around 6pm yesterday (Wednesday).

Oakhill, designed to be a secure training unit for up to 80 young offenders, was rated ‘inadequate’ in promoting positive behaviour by Ofsted earlier this month.

Inspectors had found makeshift weapons hidden in the rooms of detainees.

They were also concerned about a number of violent incidents resulting in 54 injuries to staff and inmates, with seven of the injuries serious enough to require hospital treatment.

The Ofsted report said an ‘inconsistent’ approach to violent episodes meant some perpetrators “faced little or no consequences.”

Oakhill is currently in the process of being sold off by G4S security and it is understood staff are complaining of shortages and even redundancy.

A Thames Valley Police spokesman said: “Thames Valley Police is investigating an assault at Oakhill Secure Training Centre.

“A member of staff, a 21-year-old man, was assaulted at the training centre at about 6.30pm yesterday.

“Five boys, two aged 16, one aged 15 and two aged 14, have been arrested on suspicion of assault. They are currently in police custody at this time.

“The victim is in a critical but stable condition in hospital.”