The vast majority of these cases are down to parents not following guidance on how to minimise risk.

But the researchers say that cot deaths are not investigated as thoroughly as they should be and some cases of parental abuse are being overlooked.

The researchers call on the Home Office and the Department of Health to review the way cases of cot death, or Sudden Infant Death Syndrome, are investigated by doctors and police.

They describe the current arrangements as "inadequate and in need of revision".

Cot death is the largest single category of deaths in babies over one month old.

The researchers found that in 60% of cot deaths, parents had failed to minimise the risk to their child.

In many cases they had ignored, or had failed to receive, advice such as laying their child on its back to sleep and not smoking.

However, undiagnosed maltreatment was probably the primary cause in 6% of cases.

Failings in the system

The study found that post-mortem investigations were not always thorough, diagnoses varied with the professionals involved, and medical and family histories which might prove important were not routinely available.

The report says: "As a result, it was believed that causes of death, both natural and unnatural, may be unrecognised.

"Parents may not be properly advised or supported, and uninformed speculation concerning maltreatment may arise."

The authors recommend that when an unexpected infant death occurs:

• Families are visited at home with 24-48 hours by a paediatrician or other health professional, liasing with a specially trained police officer, to gather information
• All postmortems are carried out promptly by a pathologist with specialised knowledge
• A local case review of the death by all professionals involved in the baby's care to determine cause of death, and agree a plan to support the family

Colin Baker, FSID chairman, said: "Seven babies are still dying every week in the UK, and details about the circumstances of their deaths are not being comprehensively collected.

"We could be losing valuable information that may prevent further tragedies.

"We believe we owe it to our babies to do as much as we possibly can to try to find out why cot death is still the main cause of death in infancy."

The Community Practitioners' and Health Visitors' Association (CPHVA) hailed the report as "a milestone for saving hundreds of babies' lives a year".

CPHVA's director Jackie Carnell said: "It is a blueprint to assist health visitors in their efforts to further reduce the number of deaths in babies under one year old."

The study covered 450 babies of one week to one year old who died between 1993 and 1996 in the former NHS regions of South Western, Yorkshire, Trent, Northern and Wessex.

A total of 325 of these deaths were categorised as cot death as no cause of death could be found.

The FSID and the Department of Health are producing an updated advice booklet to be distributed to expectant parents.

The FSID says that the study was carried out before its current campaign on reducing risk had a chance to take full effect.