But researchers warn that doctors often fail to recognise that a child has been deliberately mistreated.

The BBC's News24 on the new research

A team from the Departments of Child Health at the University of Wales College of Medicine and Southmead Hospital in Bristol, is calling on doctors to be more alert to the possibility of child abuse in these cases.

The National Society for the Prevention of Cruelty to Children (NSPCC), which backs the findings, says shaking a baby can leave it more damaged than a head-on road crash.

Previous injuries

Richard Hannaford on the disturbing findings of the report

The researchers want a range of mandatory tests to be carried out on infants with subdural haemorrhaging, caused by torn blood vessels.

The injury is difficult to diagnose, but can lead to death and permanent disability, such as blindness.

The research, published in the British Medical Journal, was a retrospective study of 33 children aged under two who had suffered the injury over a three-year period. Of these 28 were under 12 months old.

Three-quarters of the children died or suffered permanent disability as a result of being badly shaken.

Of the nine who died, six were dead on arrival at hospital. All had suffered previous injuries due to abuse.

Weak neck muscles

The researchers say young infants are particularly susceptible to subdural haemorrhaging because their neck muscles are weak.

Using post mortem examination reports and other techniques, they concluded that, in over 80% of the cases, it was likely the children had been intentionally abused.

Parents and carers are being warned of the dangers of shaking infants

The coroner and child protection agencies confirmed that 21 children had been abused.

The researchers believe abuse was a factor in six other cases. No clear evidence of abuse was found in five cases, although two were not properly investigated.

Many parents gave several different reasons for their child's injuries.

Most of the children were boys. The researchers suggest this is because parents think they are tougher and can withstand more shaking.

Only 22 of the children had a full range of basic investigations carried out on them, including a full blood count, a bran scan, a bone scan, an eye examination and a skeletal survey.

Mandatory tests

The researchers are concerned paediatricians may be missing many abuse cases and call for five different tests to be made mandatory for subdural haemorrhaging cases.

These are a multi-disciplinary social assessment, a test for eye nerve damage to be done by an opthalmologist, a skeletal and bone scan, a screen for blood clotting and a brain scan.

Paediatrician Dr Jean Price, one of the authors of the report, said: "We wanted to raise awareness in the public and health professionals such as health visitors and GPs as well as paediatricians that they should be more vigilant and perhaps more suspicious of this [abuse] as a cause of bleeding around the brain."

The paper will be presented to an NSPCC conference on Friday.

A spokeswoman for the organisation said the research showed the dangers of medical staff not taking child injuries seriously enough.

She added that the study coincided with other findings.

A three-year study at Alder Hey Hospital in Liverpool, for example, showed that 18 babies with subdural haemorrhaging had died and 12 had been severely handicapped.

"Shaking babies is a very, very serious thing. Some people think shaking is better than slapping a child, but it can be very dangerous," said the spokeswoman.

The NSPCC is relaunching a leaflet for parents and carers detailing the dangers of shaking babies and giving them advice about what to do if they feel they are at the end of their tether.

The organisation backs the call for mandatory tests, particularly the need for a full social assessment.

The Royal College of Paediatrics and Child Health is carrying out its own national study into the extent of shaken baby syndrome, which became headline news following the Louise Woodward case in the US.