More than a million children could be eating unhealthy lunches because their schools are exempt from tough food standards, council leaders have warned.
Academies and free schools which opt out of national regulations are failing in their moral duty to ensure pupils receive healthy dinners, according to the Local Government Association (LGA).
It said it is concerned that more than a million youngsters attending these schools could be eating poor quality dinners that do not meet national school food standards.
The LGA has issued a fresh call to the Government to introduce a single standard that applies to all schools to make sure every youngster has access to a healthy lunch.
The move comes just months before councils are due to take on more responsibility for public health, including tackling childhood obesity and overseeing the national child measurement service which takes the height and weight of children in reception and the final year of primary school.
David Simmonds, chairman of the LGA's children and young people board, said: "We know parents want school lunches that are healthy and nutritious, whatever type of school their child attends.
"School autonomy is supposed to drive up standards but in the case of school meals, we now have a two-tier system where one type of school can effectively exempt pupils from healthy choices and instead sell fatty and sugary foods.
"This threatens to seriously impact on the health and educational attainment of our children.
"As champions for parents and children, councils with new public health responsibilities will want to hold all schools to account if they are ducking their moral duty to give students the best chance of living a happy and healthy life.
"History shows us that voluntary guidelines alone do not work to drive up standards. We now need government to do its part by introducing an acceptable food standard that will allow councils to hold all schools to account for the nutritional quality of food they serve their pupils."