In 1991 the British Medical Research Council established that lack of folic acid causes two defects, spina bifida and anencephaly (an incomplete brain), but Britain has failed to make full use of the information. Since 1991 about 4,000 pregnancies have been terminated because of the defects and 250 babies have been born with severe spinal problems.
The majority would have been prevented if the women had been eating food enriched with vitamins. But enriched foods are not readily available in Britain because the Department of Health and the Ministry of Agriculture, Fisheries and Food (MAFF) have passed the responsibility for action back to the food industry and to women themselves.
Women can prevent the birth of a baby with a spinal defect by taking folic acid tablets for several months before pregnancy but relatively few do so. More than half of pregnancies are not planned and by the time women know for certain they are pregnant it is generally too late to take the tablets.
The spinal cord of the foetus develops between the 24th and 28th day following conception. So the vitamin must be taken no later than the time of the first menstrual period to have a chance of being effective.
Dr Godfrey Oakley, director of the Division of Birth Defects and Disabilities of the National Centres for Disease Control in Atlanta, Georgia, said: 'The question now is how much folic acid should be put into flour.
'If we were to restore the folic acid that is removed in milling we would put 70 micrograms (mcg) of folic acid back into 100 grams of flour - but that would not be enough to ensure that every woman got sufficient folic acid to prevent spinal birth defects.'
If twice the level needed to restore the natural vitamin were returned to flour (140mcg per 100g) then up to 75 per cent of women would get enough vitamin to prevent birth defects, according to calculations made by American government advisers.
Experts are cautious about adding more folic acid to food because it may mask the diagnosis of a rare illness, pernicious anaemia, caused by a deficiency of vitamin B12.
Dr Oakley said: 'I am not aware of anyone who has had a confusion of diagnosis as a result of taking folic acid and come to any harm. You can't kill rats with folic acid. It is completely non-toxic.'
In January the Department of Health issued advice to all women telling them to increase their folic acid intake through green leafy vegetables, through bread and cereals enriched with the vitamin, or by taking tablets available from chemists. In addition MAFF is encouraging bakers and cereal manufacturers to put folic acid in a greater range of their products.