The celebrity chef and healthy eating campaigner, Jamie Oliver, has attacked the Conservatives over their plans to end free lunches for some of the youngest primary school children.

Oliver said the “short-sighted” move would prove a mistake in the long run because it would harm children’s health and end up costing the country.

“It’s awful, it’s awful. [Theresa May] will regret it,” Oliver told Channel 4 News on Friday. “We know the diseases that the NHS are overtly paying for now and being punished for and crucified now on cost, which is largely obesity, type 2 diabetes and diet-related diseases.

“This tracks from childhood. It doesn’t just happen [during adulthood], it tracks from childhood. As far as I see it … the school is at the front line of the fight against obesity and diet-related disease.”

Oliver said he was “apolitical” on the issue, having worked with prime ministers from the Labour and Conservative parties on children’s nutrition.

The prime minister unveiled the policy on Thursday as part of the Tory manifesto. If returned to government, the party plans to end the free lunches for all but the poorest children in the first three years of primary school and provide free breakfasts for pupils instead. The party claims the policy will save about £650 per year per pupil, which will be used to increase schools funding by about £4bn over the parliament.

Oliver said: “If you speak to Mark Carney and the people at the highest level of economics, if you speak to Oxford, Cambridge university on the economic modelling of public health and the cost of ill-health and the investment, it’s the best bang for your buck you’re going to get. Don’t take from the kids, don’t take from the teachers.”

In a blogpost written after the launch of the manifesto on Thursday, Oliver said: “Obesity hasn’t just happened overnight. We’ve all heard the staggering facts that one in four British adults are obese and one in three UK kids leave primary school overweight or obese. Yet we’re continuing to walk into this crisis with our eyes now widely open, despite the impact it’s having on our health, our public services and economy.”

The Tory manifesto says the party does not believe that “giving school lunches to all children free of charge for the first three years of primary school – regardless of the income of their parents – is a sensible use of public money”.

It adds: “There is now good evidence that school breakfasts are at least as effective in helping children to make progress in school. So under a new Conservative government, schools in England will offer a free school breakfast to every child in every year of primary school, while children from low-income families will continue to receive free school lunches throughout their years in primary and secondary education.”