Concerns from parents over the safety of their children have encouraged councils to take the precaution of removing GM food from school meal menus.

According to a survey conducted last month, two-thirds of London boroughs have decided to try to block the use of GM food in school dinners, choosing to err on the side of caution.

There are also 14 county councils in England which have chosen not to use GM products, with another 20 believed to be considering introducing a ban.

Even among councils not declaring a ban there are questions over the use of GM produce and calls for more information.

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Leicester City Council has adopted a GM food ban, but neighbouring Leicestershire County Council has so far declined to join them, arguing that without better labelling of ingredients they cannot guarantee that no GM foods will be included in school meals.

The county council says that it would prefer not to use GM ingredients, but the lack of clear information about the origins of food meant that a ban could not be enforced.

Meanwhile, Leicester City Council earlier this year promised to remove GM food from schools until there was a clearer understanding of the potential risks.

The council had been lobbied to adopt the ban by the local Green Party, whose spokesman Geoffrey Forse had urged councillors to put safety first.

"We should learn the lesson of BSE. The dangers took a long time to work through and we shouldn't take any risks until we know the food is absolutely safe," said Mr Forse.

Doubts over ban

But among the London boroughs that are seeking to stop the use of GM food in school meals there are doubts about how such a ban can be put into practice.

Camden council is set to introduce new arrangements for its school dinners which will seek to remove GM ingredients. But a spokeswoman says it can be difficult for contractors to guarantee that basic items such as flour have not come from crops which have been genetically modified in some form.

The council wants food manufacturers to be required to provide complete details of the origin of their products and to offer a clear separation between GM and non-GM food.

Among the typical school meal ingredients that might have been genetically modified are soya and tomato-based products.

According to the Food Commission, which campaigns for "safer, healthier food", the London authorities which are seeking to restrict or entirely remove GM food from school meals are:

• Barnet
  Brent
  Bexley
  Camden
  Enfield
  Greenwich
  Hackney
  Hammersmith and Fulham
  Haringey
  Hillingdon
  Hounslow
  Islington
  Lambeth
  Lewisham
  Merton
  Redbridge
  Southwark
  Sutton
  Tower Hamlets
  Waltham Forest
  Wandsworth