Schools will struggle to recruit the hundreds of extra food technology teachers needed to introduce compulsory cookery classes as part of ministers' new obesity strategy.
John Howson, a teaching recruitment analyst, said although training institutions were being funded for more than 3,000 new design and technology teachers over the next three years, there was nothing ministers could do to ensure they specialised in food technology.
The Government says that 100 teachers will have been hired and trained by the end of March to help the 15 per cent of secondary schools not offering food technology. And it plans for a total of 800 teachers to go through initial training over the next three years and another 150 to come through employment-based training routes.
But Mr Howson said there was a traditional shortage because of a lack of graduates in the subject and that colleges would fill up their places with other design and technology students rather than wait for them.
John Dunford, general secretary of the Association of School and College Leaders, said there was a shortage of cookery teachers and a lack of suitable classrooms for the lessons planned for all 11 to 14-year-olds.
"The Government should never have downgraded practical cookery 20 years ago," he said. "In the intervening years, schools have been built or refurbished without practical cookery rooms, so it will be impossible for about 15 per cent of them to put cookery on the timetable until they have the proper facilities."
The TES understands that teachers' leaders have also warned ministers that they will not have the time or resources to police lunch boxes.
But a spokesman for the Department for Children, Schools and Families said: "We are not asking teachers to confiscate crisps and chocolate. We are saying, work on introducing some ground rules on what should be in lunches."
He said the Government was confident that it could recruit enough cookery teachers because of the subject's enhanced status.
The introduction of a compulsory term of food technology lessons made by Ed Balls, the Schools Secretary, and Alan Johnson, the Health Secretary, is a major U-turn. In May, Mr Johnson, then education secretary, rejected calls for compulsory cookery classes, opting instead to give an entitlement to lessons for pupils who wanted them.