Ian Huntley’s alleged attacker reportedly cried out, “I’ve done it”, after bludgeoning the child-killer with a spiked metal pole. Huntley’s head was “split in two” after he was struck six times.

Former caretaker Huntley killed 10-year-olds Holly Wells and Jessica Chapman after they left a family barbecue to buy sweets in Soham, Cambridgeshire, on August 4 2002. He dumped their bodies in a ditch.

Huntley is serving a life sentence with a recommendation he serves at least 40 years for the murders.

The Sun said the killer was knocked unconscious with a metal pole and quoted a source saying his condition was “touch and go”.

Thursday’s assault was the latest attempt on Huntley’s life. He was thought to have been kept under close observation to prevent similar attacks.

Robber Damien Fowkes slashed Huntley with a home-made weapon, causing a “severe, gaping cut to the left side of his neck” with a 7in (18cm) wound which required 21 stitches in 2010.

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Fowkes asked a prison officer: “Is he dead? I hope so.” He described Huntley as a “notorious child killer, both inside prison and in society in general”.

A Prison Service spokesperson said: “A prisoner is receiving treatment after an incident at HMP Frankland on Thursday morning. It would be inappropriate to comment further while police investigate.”

A North East Ambulance Service spokesperson said of today’s alleged attack: “We dispatched two ambulance crews to the scene and requested support from the Great North Air Ambulance Service. One patient was transported to hospital by road.”

A spokesman for Durham Constabulary said earlier today: “The 52-year-old prisoner who was injured during this morning’s assault in the workshop at HMP Frankland remains in a serious condition in hospital following treatment for head injuries.

“Police forensic teams have examined the scene of the attack throughout the day to gather evidence. A suspect, a male prisoner in his mid-40s, has been identified by officers investigating the incident.

“He has not been arrested at this stage but remains in detention within the prison.”