Parents could soon be able to check whether their children are spending their lunch money on chips.

A card could replace cash transactions in the school canteen, with parents paying to add credits to it. Details of how much pupils spend and on what would be recorded on a website, and parents could see what their children have chosen by using a password.

The initiative is the brainchild of catering firm Sodexho, which is bidding to supply meals to several schools in Oxfordshire. Menus and nutritional information is also available on its website.

Every 1 spent is rewarded with loyalty points which can be redeemed against goods such as CDs and trainers, to be bought on the web without using a credit card. By choosing healthier meals, such as salads and pasta, and water instead of fizzy drinks, pupils can earn extra points.

There is no bonus for buying chips, as they cost less than 1.

Dr Helen Lloyd, community dietician for Oxfordshire Community Health NHS Trust, said: "There are two sides to this. It is getting children to choose healthier food, but the question remains what do they class as healthy food.

She said the stigma of free school meals would be removed as all pupils would have the same type of card.