Baroness Cumberlege, parliamentary secretary at the Department of Health described the fall from 912 deaths in 1991 to 456 in 1992, as dramatic, even though there has been a decline since a peak in 1988.
She also launched a report of an expert group set up in October 1991 whose recommendations will go to all family doctors and specialists in child health.
The recommendations include that babies should be laid on their backs to sleep unless there is medical advice to the contrary; room temperatures should be around 16 to 20 degrees C and that babies should not be overwrapped and allowed to get too hot.
Dr Peter Fleming of the Institute of Child Health in Bristol, whose research with babies in Avon was the first British study to show the importance of sleeping positions, said the now discredited advice to lay babies on their fronts had been around 20 or 30 years.
'In the 1960s and 70s experience from the special care baby units was taken up around the country, without any studies taking place. In the special units they had found that very premature babies laid on their fronts seemed to do better. But what was good for tiny babies was not good for bigger babies. There was no research but it became the practice.'
Lady Cumberlege said while the reasons for cot death are still not understood and are likely to be complex, experts believe laying babies on their backs has made a significant difference.
They are now trying to tease out the relationship between babies lying prone and babies overheating as a baby on its front may be less able push away covers if it is too hot.
Dr Eileen Rubery, chairman of the Expert Group said: 'It is likely that a baby on its front cannot irradiate heat so efficiently from its face, especially if it is wearing a woolly hat at night, which could contribute to temperature rise. Being on the front is a much less flexible position,' she said.
The figures released yesterday are for the first full year since a government advertising campaign in December 1991. This was the result of pressure from campaigners, notably the television presenter Anne Diamond, whose baby Sebastian was a cot death victim.