About 2000 babies have suffered serious defects such as spina bifida since 1998 owing to the UK government's failure to add folic acid to flour, researchers have said.
These cases - around 150 a year - could have been avoided if the UK had followed 78 other countries and added the key vitamin to flour, they said.
Rates of neural tube defects - birth defects of the brain, spine or spinal cord - are not falling across the UK, resulting in death of the foetus or newborn baby, or life-long disability in those who survive.
Last month, government advisers wrote to ministers expressing their concern that recommendations made in 2000, 2006 and 2009 to improve levels of folic acid intake had still not been taken on board.
Members of the Scientific Advisory Committee on Nutrition (SACN) pointed to a rise in abortions in England and Wales for neural tube defects, with 420 in 2013, up from 390 in 2012 and 299 in 2009.
Women are urged to take 400mcg of folic acid daily while trying to conceive and for the first three months of pregnancy to cut the chance of neural tube defects, which include spina bifida and anencephaly.
However, research has found that over 70 per cent of women do not take the supplements regularly or early enough in pregnancy.
In the US, fortifying flour with folic acid has led to a 23 per cent reduction in neural tube defects.
The new research, published online in the Archives of Disease in Childhood, estimates that 2014 cases of defects could have been prevented - a 21 per cent drop - if the UK had adopted a flour fortification policy in 1998, the same year the US adopted the policy.
They said asking women to take supplements was not working and that fortifying flour was "remarkably safe".
They said: "Our results show that in the UK between 1998 and 2012, there was little, if any, change in the prevalence of pregnancies with a neural tube defect, while in the US, quickly following the introduction of mandatory fortification of flour with folic acid in 1998, there was an approximate 23 per cent reduction in the occurrence of affected births.
"Given the evidence from the Medical Research Council Vitamin Study regarding the efficacy of folic acid in preventing neural tube defects, the failure of Britain to fortify flour with folic acid has had significant consequences."
