Mothers' smoking is to blame for up to 90% of cot deaths

The scientists who carried out the research warn that motherstobe who smoke are four times more likely to see their child die from cot death than non-smokers.

The report, from Bristol University's institute of child life and health, calls on the Government to ban expectant women from buying tobacco.

Its authors say smoking in the presence of pregnant women and infants should be seen as being 'anti-social, potentially dangerous and unacceptable'. Ministers are considering whether to rewrite their advice for mothers-to-be on smoking.

Authors Peter Fleming and Dr Peter Blair based their analysis on the evidence from 21 international studies on smoking and sudden infant death syndrome.

Dr Blair said: 'If smoking is a cause of SIDS, as the evidence suggests it is, we think that if all parents stopped smoking tomorrow more than 60 per cent of SIDS deaths would be prevented.'

Around 300 babies a year die of cot death in Britain, usually between the ages of one and four months.

The report, to be published later this week, calls on the Government 'to emphasise the adverse effects of tobacco smoke exposure to infants and among pregnant women'.

It found that many women are still ignoring the risks of smoking when they were carrying a child.

'Given the power that tobacco addiction holds over its victims, there is grave concern as to whether it will be a successfully modifiable risk factor without fundamental changes in tobacco availability to vulnerable individuals,' the report says.

They say smoking may have an effect on brain chemicals in the foetus, or could prevent the lungs developing properly.

Government advice on smoking currently recommends only that mothers and fathers 'cut smoking in pregnancy'. It also says smokers should not share a bed with their baby.

Earlier this year a group of doctors called for a ban on parents smoking indoors when children are present.

Over the past 15 years, the number of pregnant mothers who smoke has fallen from 30 to 20 per cent.

However, the percentage of cot death victims whose mothers' smoked has risen from 57 per cent in 1984 to 86 per cent in 2003.

This rise is put down to the success of the Back to Sleep campaign, launched in 1991, which said parents should lay their babies on their backs to sleep.

The campaign led to a reduction in SIDS babies of three quarters and has virtually eliminated laying babies face down as a cause of cot deaths - leaving smoking as the chief cause.

Dr Blair said: 'The risk of unexpected infant death is greatly increased by both prenatal and postnatal exposure to tobacco smoke.

'We should aim to achieve a " smokefree zone" around pregnant women and infants. Reduction of prenatal exposure to tobacco smoke, by reducing smoking in pregnancy, and of postnatal exposure to tobacco, by not allowing smoking in the home, will substantially reduce the risk of SIDS.'

A spokesman for the Department of Health said they would study the report and consider whether to change their advice.