Child seats could be putting babies’ lives at risk, according to experts.

A study in the British Medical Journal says babies could stop breathing if allowed to sleep in a child seat unsupervised.

Doctors believe a lack of neck support can cause babies’ heads to flop forward, causing potentially fatal asphyxiation.

Researchers in New Zealand looked at nine babies referred to the Auckland Cot Monitoring Service who were described as ‘blue’, ‘scrunched up’ or ‘not breathing’.

Eight of these were sleeping in a child seat at home, while one was in a seat in a car.

Experts believe child seat manufacturers could modify their restraints to prevent babies’ heads from flopping forward.

Dr Michael Hayes of the Child Accident Prevention Trust said: “This study suggests in a salutary way they should not be used for hours as a substitute for a carrycot or proper cot.”