The proposal is being considered by school governors to try to improve children’s nutrition.

The National Governors’ Council has asked members to consider restricting pupils’ movements during breaks to stop them going to the sweetshop or chippie for their lunch.

The council also plans to look into limiting the choice of foods made available in school canteens to a few well-balanced meals. Primary schools will be encouraged to get rid of vending machines.

Jean McEntire, chief executive of the governors’ council, said that in the past two decades it had become acceptable to allow pupils to leave school or have unlimited choice of food in the canteen. “There is no reason why this shouldn’t be reviewed,” she said.

The proposals, contained in a joint document from the NGC and the Food Standards Agency, have been endorsed by Jacqui Smith, the school standards minister.

Ms Smith said: “It is vital that we take a whole-school approach so that nothing gets in the way of pupils’ improved education and life chances.”