Babies are consuming too much mercury, with levels that may prompt new warnings over the eating of fish.

Breastfeeding mothers and pregnant women have already been advised to limit their intake of species such as shark, swordfish and tuna because of the risk of damaging the nervous systems of their offspring.

But new estimates of mercury levels indicate that babies between four and 12 months old are, in some cases, consuming twice the amount that the US environmental protection agency and British advisers deem safe for adults.

The committee of toxicity in food is considering further action because the concentration of mercury in baby food may be twice as high as suggested in a survey in the late 1990s, although this may be due to more fish-based products being included in the more recent checks .

The committee will also consider whether concentrations of zinc, nickel and arsenic in the diet of infants, which also exceed relevant safety guidelines in some cases, pose a risk.

A push to cut levels of lead is already under way. The survey indicates that lead levels in infant food are relatively low and have probably fallen.

Officials say such estimates should be treated with caution, questioning whether adult safety margins can be usefully applied to children, and point out the inability to distinguish between inorganic mercury and methylmercury, which has prompted wider concerns over oily fish.

The mercury warning comes just weeks after advisers questioned the safety of soya-based infant formula milk, fearing it may affect children's sexual development and later fertility.

The latest twist over mercury in fish coincides with a more wide-ranging review. The current view is that most Britons do not eat the weekly portion of oily fish, such as mackerel, herring, sardine or trout, which helps to ward off heart disease. But contam inants from polluted seas and rivers now found in fish are causing rising concern.