Bradford parents have been urged not to sleep with their babies on the sofa or in bed to avoid causing death by overlaying or cot death.

Bradford coroner Roger Whittaker issued this warning in light of new research carried out by researchers from the Royal Hospital for Children in Bristol.

The research published in The Lancet has shown that there has been a fourfold increase in the number of co-sleeping deaths on the sofa.

Mr Whittaker said: "Do not do it - it's as simple as that. In Bradford we have had far too many cases of children who have died unnecessarily."

Mr Whittaker stressed that there was a difference between deaths from Sudden Infant Death Syndrome (SIDS) or cot death and deaths caused by overlaying.

"Overlaying is something that is an accident that it totally avoidable whereas deaths from SIDS or cot death probably could not have been avoided," he said.

Mr Whittaker urged parents who were tired, had been drinking or smoking specifically not to co-sleep because of the increased risk.

Dr Chris Day, consultant neonatal paediatrician at Bradford Teaching Hospitals, said: "This research confirms what we already know and the advice we are already giving out to parents."

Dr Day said there was an increased risk of death if a parent slept with their baby on a sofa. He also urged parents to return babies to their cot after feeding to eliminate any risk.

The research led by Professor Peter Fleming found that although the number of deaths in the parental bed had fallen, there had been an increase in the number of sudden infant death syndrome cases occurring when a parent sleeps with a baby on a sofa.

Professor Fleming said: "Although the reasons for the rise in deaths when a parent sleeps with their infant on a sofa are unclear, we strongly recommend that parents avoid this practice."

The risk of SIDS is higher for male, premature and low-birthweight babies and those sleeping on their side or front. Smoking during pregnancy and exposure to secondary smoke after birth can also increase the risk of SIDS.

Dr Day said: "Smoking during pregnancy or exposure to smoke after pregnancy is an important avoidable risk for cot death."

The study looked at data on 369 SIDS cases which occurred between 1984 and 2003 in Avon. These were compared to information on 1,300 healthy babies from a study carried out between 1993 and 1996.