Shocking details of techniques used to inflict pain deliberately on children in privately run jails have been revealed for the first time in a government document obtained by the Observer.

Some of the restraint and self-defence measures approved by the Ministry of Justice include ramming knuckles into ribs and raking shoes down the shins. Other extraordinary passages in the previously secret manual, Physical Control in Care, authorise staff to:

■ "Use an inverted knuckle into the trainee's sternum and drive inward and upward."

■ "Continue to carry alternate elbow strikes to the young person's ribs until a release is achieved."

■ "Drive straight fingers into the young person's face, and then quickly drive the straightened fingers of the same hand downwards into the young person's groin area."

The disclosure of the prison service manual follows a five-year freedom of information battle. The manual was condemned last night by campaigners as "state authorisation of institutionalised child abuse".

Published by the HM Prison Service in 2005 and classified as a restricted government document, the manual guides staff on what restraint and self-defence techniques are authorised for use on children as young as 12 in secure training centres. The centres are purpose-built facilities for young offenders up to the age of 17 and run by private firms under government contracts.

Instructions to staff warn that the techniques risk giving children a "fracture to the skull" and "temporary or permanent blindness caused by rupture to eyeball or detached retina".

The guidance, designed to cope with unruly children, also acknowledges that the measures could cause asphyxia. One passage, explaining how to administer a head-hold on children, adds that "if breathing is compromised the situation ceases to be a restraint and becomes a medical emergency".

Carolyne Willow, national co-ordinator of the Children's Rights Alliance for England (CRAE), which led the campaign for disclosure following the deaths of two teenage boys in secure training centres, said: "The manual is deeply disturbing and stands as state authorisation of institutionalised child abuse. What made former ministers believe that children as young as 12 could get so out of control so often that staff should be taught how to ram their knuckles into their rib cages? Would we allow paediatricians, teachers or children's home staff to be trained in how to deliberately hurt and humiliate children?"

The campaign for publication began following the deaths of Gareth Myatt and Adam Rickwood. Myatt, 15, died while being held down by three staff at Rainsbrook Secure Training Centre in Warwickshire. Myatt choked on his own vomit and died.

In the same year, 2004, 14-year-old Rickwood, from Burnley, hanged himself at the Hassockfield Secure Training Centre in County Durham. A judge ruled last year that the carers who restrained Rickwood shortly before his death had used unlawful force.

His mother, Carol Pounder, was said to be "relieved" that other parents would now know the truth behind the use of restraint.

Deborah Coles, co-director of the charity Inquest, which campaigns on the issue of contentious deaths in custody, claimed their deaths emanated from a "culture of obfuscation, secrecy and complacency… in which dangerous, unlawful and ultimately lethal practices continued unchecked".

Earlier this month the government was prepared to go to a tribunal to fight against the disclosure of the manual, despite the information commissioner ruling that the public interest was so grave the document should be released. The Ministry of Justice backed down and last week released the entire 119-page document. Previously, officials had even refused to give a copy to the parliamentary human rights committee.

Phillip Noyes, director of strategy and development at the National Society for the Prevention of Cruelty to Children, said: "These shocking revelations graphically illustrate the cruel and degrading violence inflicted at times on children in custody. On occasions these restraint techniques have resulted in children suffering broken arms, noses, wrists and fingers. Painful restraint is a clear breach of children's human rights against some of the most vulnerable youngsters in society and does not have a place in decent society."

One former manager of a secure children's home with almost 20 years' experience said the revelations were "horrifying" and described the self-defence techniques as "child abuse".

"Nose distraction" techniques – sharp blows to the nose – have already been found by the Court of Appeal to have been routinely and unlawfully used in at least one centre.

The legal director for CRAE, Katy Swaine, said the contents of the manual offered evidence that the treatment of children in secure training centres had contravened human rights laws. She said: "The guidance given in this state-authorised manual violates human rights because it allows staff to deliberately hurt children outside cases of life-threatening necessity."

During the 12 months up to March 2009, restraint was used 1,776 times in the UK's four secure training centres.

Sir Al Aynsley-Green, the former children's commissioner for England and emeritus professor of child health at University College London, said: "It's time the whole country knows what is going on under their noses. This is just part of a brutal system, and we welcome the fact this is finally in the open."

Malcolm Stevens, a former government policy adviser and director of secure training centres who helped to develop the government's guidance for staff working in secure centres during the 1990s, said he could not understand why pain-inducing techniques were endorsed. He said: "I have never seen the need to use pain-compliant techniques, and after 15 years my view has not changed. I have no truck with distraction techniques."

The document also describes the application of steel handcuffs: children are forced to "adopt a kneeling position" while a second staff member "takes control of the head" by grabbing the back of the neck while cupping the chin.

Willow, who has drawn up 30 parliamentary questions to be tabled by MPs this week to ascertain how many times these self-defence techniques have been used in the past five years, said: "The ritualistic humiliation of making children kneel down to get handcuffs on and off is truly sickening and a clear abuse of human rights. Techniques include holding a 'child's forehead to the floor with another hand on the back of the neck'."

The Ministry of Justice said: "For young people under 18, the use of restraint is always a last resort. But where young people's behaviour puts themselves or others at serious risk, staff need to be able to intervene effectively, to protect the safety of all involved." The ministry added that the manual "is an aid for instructors" who train staff on the use of restraint techniques.