Researchers who studied almost 400,000 infants born in Taiwan found that high levels of chlorine by-products in tap water could affect the development of babies in the womb.

A significant impact was seen on the likelihood of babies being born with three common but serious types of abnormality.

They were ventricular septal, or "hole-in-the-heart" defects, cleft palate, and anencephalus - a condition that causes much of the brain, skull and scalp to be missing at birth.

The by-products linked to these defects are called trihalomethanes.

Tap water concentrations of the chemicals above 20 micrograms per litre were associated with a 50-100% higher level of risk than concentrations below five micrograms.

The findings, from a team led by Professor Jouni Jaakkola at the University of Birmingham, were published in the journal Environmental Health.

All public-supply tap water is chlorinated in the UK to get rid of bugs that can cause diseases such as cholera and typhoid. However the trihalomethane content of tap water varies according to its source.

Water that has run off farm land and contains a lot of organic chemicals is more likely to contain the by-products.

The Drinking Water Inspectorate (DWI), which acts as the guardian of water quality on behalf of the Department for Environment, Food and Rural Affairs (Defra), said its own research had been unable to confirm a link between trihalomethanes and birth defects.