Cot deaths are more common at weekends and holidays, according to official statistics.

It is thought that this could be partly due to disruption to routine and changes in where the baby sleeps.

The study by the Office for National Statistics found that between 1993 and 1998, 1,431 babies died from Sudden Infant Death Syndrome (SIDS) during the week and 705 at the weekend or on a public holiday.

Fifty more babies than expected died on Saturdays, Sundays and holidays.

The trend is not seen in other deaths among older infants aged 28 days to a year.

Report author Nirupa Dattani said: "It could be attributed to a number of factors, including changing parental routines, changes in the environment or a reluctance to seek help for what could be a trivial illness."

Cot deaths fell by a third between 1993 and 1998, while the overall infant mortality rate decreased by a tenth.

The reduction in cot deaths was mainly due to better guidance about how babies should sleep to avoid the risk of SIDS.

In 1998 280 babies in England and Wales died from SIDS, compared with 453 in 1993.

The report found that low birth weight babies, twins and triplets, and children born outside marriage are at increased risk of cot death.

More than 60% of deaths from SIDS occur in babies where the parents are not married, according to the ONS.

There are also regional variations in the rate of cot deaths, the study revealed.

The North West has consistently had the highest SIDS rate while South Thames boasts the lowest.

Joyce Epstein, secretary general of the Foundation for the Study of Infant Deaths, said nobody really knew why some babies died.

She said: "We need to know much more about the babies who are dying.

"Currently, important details about their deaths are not being collected and analysed nationally, so vital information is being lost that could save other babies' lives.

"Cot death claims seven lives every week in the UK and it remains the main kind of death in babies over one month old.

"We need more research to bring an end to these tragedies."

Sudden infant death syndrome is a term used when a baby has died of an inexplicable cause.

A recent study concluded that six out of ten cot deaths could be partly caused by sub-standard care, deprived living conditions or abuse.