Under the plan, all bread would be made with folic acid-fortified flour

The proposal will go before the board of the Food Standards Agency next week for ratification.

If passed, ministers will then decide whether to press ahead.

Scientific research shows that folic acid significantly cuts the risk of neural tube defects, which affect up to 900 pregnancies a year in the UK.

However, there is concern that adding the vitamin to flour could harm some elderly patients, as it could mask a deficiency in the B12 vitamin.

Up to 10% of those aged 65 and older have borderline B12 levels and could tip into deficiency.

In extreme cases, this can cause irreversible damage to the nervous system.

The recommendation to the FSA board suggests that products containing folic acid at nutritionally significant levels should be clearly labelled.

It also argues that mandatory fortification should be accompanied by new controls on the voluntary addition of folic acid to other products, such as breakfast cereals and low-fat spreads, and on the use of folic acid supplements.

A system for monitoring the health impact of fortification would also be needed.

Unplanned pregnancies

Wholemeal flour would be exempt from fortification in order to give consumers more choice.

The FSA already advises women to eat extra folic acid when trying to get pregnant.

However, research suggests that only half of such women adhere to this advice.

Also, up to half of pregnancies are unplanned, meaning women may miss the opportunity.

Each year between 500 and 600 babies in the UK are reported to have neural tube defects. It is thought many of the other affected pregnancies are terminated.

Mandatory fortification has already been introduced in the USA, Canada and Chile, where it cut NTD rates by between 27% and 50%.

A panel of UK experts, the Scientific Advisory Committee on Nutrition (SACN), last year backed mandatory fortification of flour.

SACN found no evidence that vitamin B12 deficiency was masked in older people, provided folic acid doses were 1mg a day or less.

An FSA consultation on the issue drew 202 responses from industry, consumer groups and individuals.

The baking industry raised "practical concerns" about the fortification of bread.