According to the Office of National Statistics, the number of babies dying from cot death fell by 6% last year, to 231.

The Foundation for the Study of Infant Deaths (FSID) does not dispute that, overall, the figure has plummeted over the past 12 years.

The system for responding to sudden infant deaths is inadequate and unfair to bereaved families

Dr Richard Wilson, trustee, FSID

This is mainly due to the advice given to parents, starting from 1991, to always lie babies on their backs in their cots.

However, falls in more recent years may be due more to the way deaths are counted than a genuine improvement, it says.

There has been a 250% increase in the number of deaths whose cause is described as "unascertainable" by coroners.

These deaths are not counted as cot deaths in official statistics - there were more than 80 of them last year alone.

As far as the Foundation is concerned, a death with an "unascertainable" cause is, to all intents and purposes, a cot death.

Both involve the sudden and unexpected death of a baby, with no obvious cause at post mortem.

FSID believes that not only does this trend disguise the true level of cot deaths in the UK, but is likely to confuse and distress parents whose baby has died under such circumstances.

It is calling for stricter rules so that a single description can be applied.

Upsetting

Dr Richard Wilson, a consultant paediatrician and FSID trustee, said: "The system for responding to sudden infant deaths is inadequate and unfair to bereaved families who can be desperate to understand why their baby died.

Advice to reduce cot death risk

Most important: Put babies to sleep on their backs Cut smoking in pregnancy - this applies to both fathers and mothers Do not let anyone smoke in the same room as your baby Keep your baby's head uncovered - place your baby with feet to the foot of the cot, to prevent wriggling down under the covers Sleep your baby in a cot in your room for the first six months Do not share a bed with your baby if you or your partner are smokers, have been drinking alcohol, take drugs or medication that makes you drowsy or are excessively tired

"A postcode lottery means that families will be given different answers for why their baby died depending on where they live.

"Parents are left confused and national statistics are unreliable.

"Pathologists with special training in babies, and working to national protocols, should examine all babies who die."

However, there is no disguising the success of campaigns to raise public awareness of the risk of cot death.

In 1988, prior to the "on the back" advice to parents, the sudden infant death rate was 2.3 per 1,000 babies.

Now it is 0.39 per 1,000.