The largest ever study of cot deaths in the UK has found that babies born into poor families are at a far greater risk than those born to better-off parents.

The report calls for health promotion efforts to be targeted at vulnerable families, and urges the Home Office and the Department of Health to review their 'inadequate' arrangements for investigating infant deaths.

Report editor Peter Fleming, professor of infant health and developmental psychology at Bristol University, told H S J that the national Back to Sleep campaign in 1991 - which led to a 70 per cent fall in cot deaths - had failed to reach families most at risk. 'In a middleclass non-smoking family, where the mother is over 25 and is supported by a partner, the risk is one in 8,500. In a low-income family where the mother is under 25, a smoker and unsupported by a partner, the risk is one in 200.'

An expert review panel concluded that neglect or parental abuse was the probable cause of some deaths put down to sudden infant death syndrome.

The report recommends that all families should be visited at home within 2448 hours of an unexpected infant death by a health professional liasing with a specially trained police officer.

Pathologists with special training in paediatric pathology should conduct post-mortems, and a multidisciplinary case review should establish cause of death and support the family.

The study, by the Confidential Enquiry into Stillbirth and Death in Infancy, covered 470,000 births and looked in detail at the cases of 450 babies who died between 1993 and 1996. It found that falling asleep with a baby on a sofa increased the risk of cot death almost 50-fold - probably because of the heat generated by the adult's body.

Sharing a bed with the baby was also a risk if the parent smoked, had recently drunk alcohol, or taken drugs that reduced awareness.

But immunising the baby and keeping its cot in the parents' bedroom for six months were both protective factors.

Dr Liz Scott, director of public health at Leeds health authority, welcomed the report but said giving health professionals the lead in investigating infant deaths was 'something we should discuss. . . it's a minefield.'

Sudden Unexpected Deaths in infancy: the CESDI SUDI Studies 1993-1996.

The risk factors Young mother.

Large number of children in family.

Low income.

Smoking in the home.

Poor housing.

Baby of low birth weight .

Baby with congenital abnormality.