Pregnant women who regularly use mobile phones could increase the risk of their children behaving badly, claims a startling survey.

If their offspring then start using the devices at an early age, the chance of problems climbs to 50 per cent, according to researchers.

They found those exposed to mobile phones in the womb had a 30 per cent rise in behavioural difficulties at the age of seven.

Pregnant pause: Researchers suggest that pregnant women who regularly use mobile phones are putting their babies at risk of developing behavioural problems

But those exposed before birth and in their childhood, were 50 per cent more likely to have behavioural problems than those exposed to neither.

Children who used mobiles, but were not exposed in the womb, were 20 per cent more likely to display abnormal behaviour.

The findings by researchers in California are likely to reinforce warnings that children should not use mobile phones.

However, some British scientists were sceptical, saying the findings may be due to lifestyle factors rather than mobiles.

In the study of 29,000 youngsters, mothers provided details of their lifestyle, diet and environment during and after pregnancy.

Information on their childrens health and mobile phone use was also recorded. Around three per cent of children scored abnormal on behavioural issues, with another three per cent borderline.

The study found that more than ten per cent of children exposed to mobile phones in the womb had mothers who spoke on them at least four times a day.

Nearly half of the mothers had their phones turned on at all times while around a third of children were using a mobile phone by the age of seven.