MPs have rejected a plan to extend free school meals into the school holidays by 322 votes to 261.
The Labour motion, which was defeated by a majority of 61, would have extended provision of hot food for children until Easter 2021.
Boris Johnson had whipped Tory MPs to vote against the plan, arguing that it was not the job of schools to “regularly provide food during the school holidays”.
More than 1.4 million children experience food insecurity during the holidays, according to the Food Foundation, while 6.3 per cent of children are worried about going hungry during the impending October half-term.
Campaigners say the extra provision is needed because the coronavirus crisis is leading to a surge in economic insecurity, with unemployment expected to spike dramatically in the coming months as the second wave of the disease hits.
The government previously bowed to pressure and extended meals over the summer holidays, but says it does not want to do so again.
Kate Green, the shadow education secretary, said Mr Johnson and the Conservatives had “badly let down more than 1 million children and their families”.
“No child should go hungry over the holidays, but the government is blocking the action needed to prevent this,” she said.
“We pay tribute to Marcus Rashford and others for shining a spotlight on this incredibly important issue. This campaign is not over and the government must reconsider.”
The campaign to extend school meals was initially spearheaded by footballer Marcus Rashford, who forced the government into the U-turn on the summer break.
“A significant number of children are going to be tonight not only hungry but feeling like they do not matter because of comments that have been made today,” he said, adding that the issue was not a question of politics but of “humanity”.
A handful of Conservative MPs rebelled against the government’s whip, but the vast majority backed it.
Speaking during the debate, Brendan Clarke-Smith, Tory MP for Bassetlaw, said: “I ask, when did it become controversial to suggest that the primary responsibility for a child’s welfare should be with their parents?”
Ben Bradley, Tory MP for Mansfield, explained his reasoning in voting against the motion, arguing that extending free school meals “passes responsibility for feeding kids away from parents, to the state”. He added: “It increases dependency.”
Conservative minister Therese Coffey, who was speaking for the government, urged MPs to reject the plan, but claimed that “social justice has been at the absolute heart of every decision that this government has taken in order to help the people of this country get through the pandemic together”.