According to the Foundation for the Study of Infant Deaths (FSID), 89 per cent of all cot deaths in England and Wales occur in babies aged under six months. Boys appear to be at higher risk than girls.

But the number of cot deaths in Britain has fallen by nearly 70 per cent since the introduction in the 1990s of initiatives to cut risk factors.

This decline has been mirrored around the world, with cot death rates halving as a result of “Back to Sleep” campaigns, which claim that putting a baby to sleep on its back reduces the danger.

Various factors appear to increase the risk. If a mother is under 27 and had more than one previous child, and if both parents smoked and were unemployed, the chance of cot death was around one in 200.

But if these factors were absent, the likelihood was far lower — about one in 8,500.

The risk also increases if the family has already suffered a cot death, FSID says. Joyce Epstein, FSID director, said: “Second cot deaths can be true cot deaths, where all other causes have been excluded.”

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