Light drinking in pregnancy does babies no harm in the long run, according to a substantial new study which challenges the government's advice that women should abstain completely for nine months.

The study showed that the children of mothers who drank one or two units of alcohol a week during pregnancy have suffered no ill-effects by the time they are five. They do not have behavioural difficulties and nor are they behind in their intellectual development.

The work is published online today in the Journal of Epidemiology and Community Health. It should help to give women credible information on which to base their choice, said joint author Dr Yvonne Kelly of University College London's department of epidemiology and public health.

"This isn't about heavy consumption or foetal alcohol syndrome in any sense or about binge-drinking," said Kelly. "It is about the occasional drink and whether that is associated with developmental problems."

She did not want to comment on the current advice from government. "I'm not sure we're in the business of acting as advocates but if women have information, it is plausible that they can make informed choices," she said.

The study is based on a large sample from the millennium cohort study – 11,500 children who were born between September 2000 and January 2002. The mothers were interviewed in person about their drinking patterns while they were pregnant.

They were placed in one of five categories: teetotal; those who drank but not in pregnancy; light drinkers (one to two units per week); moderate (three to six units a week or three to five at one sitting); and binge or heavy drinkers (seven or more units a week or six at one sitting).

Just under 6% of the women never drank and 60% abstained during pregnancy. Just under 26% said they were light drinkers, 5.5% were moderate drinkers and 2.5% were binge or heavy drinkers.

The team have already published their results for children up to the age of three. The latest paper follows them to the age of five, to ensure there is no "sleeper" effect of the alcohol their mothers drank during pregnancy.

They found that children whose mothers had been heavy drinkers were more likely to be hyperactive and have behavioural and emotional problems than those whose mothers abstained during pregnancy.

But there was no evidence to suggest that the children of light drinkers, whose mothers had no more than the odd glass of wine a week, had been in any way harmed.

Women who drank occasionally tended to be from more advantaged socioeconomic backgrounds, which the authors took into account in their calculations.

Their children were 30% less likely to have behavioural problems and had higher scores in mental development tests than those of women who abstained in pregnancy.

But the government reiterated its advice that pregnant women should not drink at all.

"After assessing the available evidence, we cannot say with confidence that drinking during pregnancy is safe and will not harm your baby," said a spokesperson.

"Therefore, as a precautionary measure, our advice to pregnant women and women trying to conceive is to avoid alcohol."

Dr Anthony Falconer, president of the Royal College of Obstetricians and Gynaecologists, said current evidence showed one to two units a week was acceptable. The key public health message is that "light drinking is fine but heavy and binge drinking should be avoided", he said.

"Anecdotally, the majority of women are responsible and tend to stop drinking once they find out they are pregnant," he said. "But with rising levels of binge drinking among younger women, we are concerned about those who find it difficult to wean themselves off alcohol, as heavy, sustained drinking will damage the foetus.

"These women should be given the support they need, not just during pregnancy but in the longer term."