BRITONS have been told to eat more oily fish to combat heart disease, make them brainier and prevent them going insane. But the nation should play safe and not gorge itself on dinners of salmon, trout, mackerel, sardines, pilchards, herrings, kippers, eel and whitebait.

This twin call from the Food Standards Agency is intended to ensure that the benefits of eating fish are not outweighed by the risks of consuming toxins such as mercury and other dioxins found in oily fish. But the overall message from the watchdog is that fish is safe and that most people would improve their health by eating much more than they do now.

The agency has recognised concerns over various dioxins and has imposed limits on oily fish consumption. But they far exceed the amounts of oily fish currently eaten in Britain.The general guidance is that everybody should eat one portion of white fish and one of oily fish each week, yet most of the country eats less than a third of an oily fish portion a week and some 70 per cent eat none at all.

In future oily fish can safely be on the menu as many as four times a week for men, boys and women above child-bearing age, while for pregnant women, those hoping to be so, breastfeeding mothers and girls, oily fish can easily be eaten twice a week without any additional health risk.

Levels of dioxins in fish vary and are highest in herring while low in trout. However, dioxins and polychlorinated biphenyls (PCB), once used in elecrical equipment that was dumped at sea but which have not been manufactured since the 1970s — are environmental pollutants linked to various cancers and can build up in the human body over a long period of time. They can also build up by eating milk, meat and eggs, though dioxins in food generally in Britain have fallen by 70 per cent in the past ten years.

The new advice about eating oily fish was given yesterday by Sir John Krebs, chairman of the FSA, after advice from experts on the Scientific Advisory Committee on Nutrition and the Committee on Toxicity of Chemicals.

Health experts are anxious that most people gain the health benefits of Omega 3 fatty acids that are present in oily fish in particular. These help to ward off heart disease, are essential for the development of the brain in babies and young children, can improve intellect and help to fend off mental illness.

Omega 3 fatty acids are also found in egg yolks, linseed and hempseed.

The advice is a fillip to the Scottish salmon industry which experienced a dip in sales in the new year after American scientists said that farmed salmon caused cancer and that Scottish fish were so contaminated with pollutants that it should not be eaten more than three times a year.

The limits on eating oily fish were criticised by Michael Crawford, director of the Institute of Brain Chemistry and Human Nutrition at London Metropolitan University.

“I really don’t believe in these limits, it’s hocus-pocus and suggests that there is a hidden threat. The Japanese and the Icelanders eat more fish and seafood than anyone else and they have the longest life expectancy and the highest birth weights. We should eat as much as we like and it will not do us any harm.

“It will also improve the health of the nation which is suffering chronic heart disease and an epidemic of mental illness and psychiatric disorders.”

A recommended portion is about five ounces (140g) of cooked fish and six ounces (170g) of raw. Canned tuna does not count as an oily fish — other canned species do — but like white fish it also contains Omega 3 fatty acids.

• Mothers who want brighter children should eat fish regularly during pregnancy, according to new research from the University of North Carolina.

  Children aged 15 months were tested for their understanding of words and those with mothers who ate fish more than once a week scored 7 per cent higher than those who ate no fish.

  Similar patterns were seen in tests on social activity and language development. Children who ate fish once a week before their first birthday also scored higher.

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