Sharing a bed increases the risk of sudden infant death
Parents are being warned not to risk their babies' lives by sharing a bed with them while sleeping.
Latest evidence released by the Foundation for the Study of Infant Deaths (FSID) shows bed sharing is implicated in about half of cot deaths.
The risk is greatest if either parent smokes, has been drinking, has taken sedative medication or is "very tired".
Even without these factors, the charity said that the safest place for a baby to sleep was its own cot.
Small babies - those born prematurely and those weighing less than 2.5kg are particularly at risk.
FSID's director, Joyce Epstein, said: "We recognise the urgent need to raise awareness of the dangers associated with bed or sofa sharing with your baby.
"It's fine to breastfeed in bed, but if you smoke at all - even if not in the bedroom - or you've drunk alcohol - you really must protect your baby and put them in their cot to sleep."
John Pollard, a coroner for the Manchester South District, said he saw many families whose lives had been devastated by the sudden death of their baby.
"The numbers of infants that we continue to find dead in beds, on sofas or armchairs is unacceptable.
"We need to make all parents aware that the most comfortable place for them to sleep is the most dangerous place for their baby."
Data from Dr Marta Cohen, paediatric pathologist at Sheffield Children's Hospital, showed that of the 50 cases she investigated between 2004 and 2007, 31 were found to have been sharing a bed or sofa with a parent.
Dr Chris Wright, consultant perinatal pathologist at the Royal Victoria Infirmary, Newcastle, examined 15 cases of unexpected death in infants between 2008 and 2009 - seven were found in the parental bed and two had died on a sofa.
In the London area between 2005 and 2008, 173 babies died suddenly and unexpectedly. And 85 of these infants were found dead after falling asleep in bed with an adult or on a sofa.
But the Royal College of Midwives said catch-all advice was unhelpful to parents.
The college's Cathy Warwick said: "It is a terrible tragedy for the parents when they suffer the sudden death of their child, so any research that sheds light on the potential causes is important.
"However, the situation around co-sleeping is complex, and blanket advice to avoid it is perhaps unhelpful to parents who may want to do it.
"A number of factors need to be considered by parents before and if they do this, and they need to discuss this with their midwife to make an individual and informed decision."
The RCM says many factors can contribute to the safety of co-sleeping, including cultural practices, whether the baby is being breastfed, what kind of bedcovers are being used, and where the co-sleeping is taking place.
It recommends that parents discuss the issue with their midwife, and that based on the evidence they can make an informed choice about co-sleeping.
The RCM has also issued guidance on bed sharing and co-sleeping.