A cot death charity has raised concerns about so-called "baby boxes" which are used for infants to sleep in.
The concept of a baby box originates from Finland where new parents are given a cardboard box filled with baby products and a mattress - the box itself can then be used as a bed.
The tradition, which has been taken up by a number of NHS organisations, has been cited as helping reduce the rate of sudden infant death syndrome (SIDS), also known as cot death.
But now The Lullaby Trust, which works to reduce SIDS, has said there is no evidence to support the claim the boxes reduce infant mortality.
It acknowledged that for some parents, who do not have an enclosed space for their baby to sleep such as a cot or Moses basket, a box may be a better alternative than a baby sleeping in a "hazardous" condition.
The charity has also claimed it is not possible for baby boxes to fully comply with safety standards.
The charity said British and EU safety standards for nursery furniture only exist for traditional cots, cribs and bassinets and there is currently no specific standard for the use of a cardboard box as a sleeping place for an infant.
It also raised questions over the safety of the mattresses in some boxes available on the market and has advised parents to check that these meet safety standards before using them.
Francine Bates, chief executive of The Lullaby Trust, said: "We support all efforts to promote safer sleep for babies, however we do have concerns about the baby boxes being marketed as products which will reduce infant mortality and SIDS.
"We are not aware of any evidence, including in Finland, to support this claim.
"It is also not possible for baby boxes to meet all current safety standards, as nursery furniture regulations only apply to traditional cots, cribs and bassinets, not boxes made from cardboard.
"If parents choose to use the box to sleep their baby, we urge them to read and follow our advice, approved by our scientific and paediatric advisers."
The charity has urged health and social care professionals who distribute the boxes as well as parents who are considering using or purchasing a baby box to ensure the box and also the mattress supplied comply with British and European Standards and existing UK fire regulations.
It has said that it will no longer allow its branded leaflets to be enclosed with baby boxes "as this suggests we endorse the product".
In new advice for parents, the charity also said that if a parent does decide to use a box it should be used for "daytime naps only", with a baby sleeping in a cot or a Moses basket next to their bed during the night.
It also reminds them not to lift or carry the box around your home if a baby is in it.
SIDS, also known as cot death, is the sudden unexplained death of an apparently healthy baby.
There were 230 sudden infant deaths in the UK in 2014, following a downward trend in the last decade. In 2001, there were 330.