TV chef Jamie Oliver has accused Education Secretary Michael Gove of "eroding" healthy school food standards.
The celebrity chef expressed concern that academy schools are not obliged to sign up to food standards introduced by the previous government.
In an interview with the BBC, Oliver urged parents to tell Gove not to change the rules, warning that a move away from them would be a "disaster".
"The bit of work that we did, which is law, was a good bit of work for any government. So to erode it, which is essentially what Mr Gove is doing - his view is we let schools do what they want," Oliver said in the interview.
Oliver said he thought implementing food standards in schools was "a wonderful ambition", but acknowledged that head teachers are pushed more than ever and expected to do more, describing them as having to be "entrepreneurial caterers as well as everything else they have to do".
"The standards are there to really keep everyone on their game. It's not a large amount of paperwork, it really isn't and, for what it's for, which is essentially the future of our country, it's really important," he said.
According to the latest official figures, more than two-fifths of primary school children and a third of secondary school pupils are now opting for school meals.
The take-up for healthy school meals has been growing since Oliver's school meals revolution began about six years ago, when he campaigned for better quality school meals.
The campaign gained extensive public support and led to strict nutritional guidelines for meals, which were introduced to primary schools in 2008 and secondary schools in 2009.
But academies, which are semi-independent state schools, are not obligated to sign up and, since last year, the government has permitted any school to apply for academy status.
"I think the Conservatives have been very clever, because if they just came out and said 'we're taking away the standards'... what they've done is they're actively, aggressively pushing academies, which is already one-third of all our secondary schools, and they don't have any requirements at all," Oliver told BBC News.
"I think parents need to tell Mr Gove that the standards are there for good reason and, actually, not everything that the last government did was wrong. They did a lot of good stuff and he shouldn't touch them. It could be a disaster," he said.
He explained that for 190 days of the year, from the age of four, many children have both breakfast and lunch at school. "The government is in control of... half of your child's childhood nutrition," he said.
Oliver warned that Britain is "in the middle of the darkest health moment in British history as far as kids' health is concerned".
He said he felt it was important for him to represent parents and speak up on their behalf, because of the rising concerns surrounding child and adolescent obesity and the pressure it is placing on the health system.
Quoting official figures, Oliver said obesity was costing Britain £4 billion a year.
"We can't afford it, we can't afford it," he protested. "I'm really worried."
Twenty-five per cent of children under 10 are obese, along with a third of teenagers.
"We're the most unhealthy in Europe," Oliver said.