Hungry children are sitting in class worrying about what their younger siblings will eat at home later, says campaigning footballer Marcus Rashford.
Rashford, who prompted a Westminster government U-turn on free meals over the summer holidays, says some cannot focus due to rumbling stomachs.
Stepping up his child poverty campaign, he is urging UK ministers to offer free meals to 1.5 million more children.
Number 10 said it was not for schools to provide food during holidays.
The Prime Minister’s official spokesman told reporters the government had already “taken action to make sure children don’t go hungry”.
“We are in a different position now schools are open – it’s not for schools to regularly provide food during the holidays.
“We think Universal Credit will provide what’s needed,” he added.
Wales has said it will offer poor pupils free meals over the holidays.
Northern Ireland, which has announced a time limited lockdown in which schools will close, has said it will cover pupils’ meals during this period, but nothing further is promised for the coming Christmas holiday.
England’s government has not committed any further resources to free school meals since schools returned in September.
Rashford, who has told of his own impoverished childhood and formed a coalition of food campaigners under the name #endchildfoodpoverty, is now mounting a petition to Parliament.
The petition calls for free school meals to be available for every child from a household on Universal Credit or equivalent.
This would mean the meals reach an additional 1.5 million children aged seven to 16, his campaign said.
He also wants holiday meals and activities to be expanded to an extra 1.1 million, and the value of healthy food vouchers for pregnant women to be increased to increased to £4.25 per week (up from £3.10)
Rashford, who has just become an MBE for his work for vulnerable children, said many say that education is the most effective means of combating poverty.
But he added: “Education is only effective when children can engage in learning.
“Right now, a generation who have already been penalised during this pandemic with lack of access to educational resources are now back in school struggling to concentrate due to worry and the sound of their rumbling stomachs.
“Whatever your feeling, opinion, or judgement, food poverty is never the child’s fault.
“Let’s protect our young. Let’s wrap arms around each other and stand together to say that this is unacceptable, that we are united in protecting our children.”
He added that millions of British children were finding themselves in very vulnerable circumstances, and were “beginning to question what it really means to be British”.
“I’m calling on you all today to help me prove to them that being British is something to be proud of,” he said.
Rashford added: “The school holidays used to be a highlight of the year for children. Today, it is met with anxiety from those as young as seven years old.”
Saffron, who is 15 and from Portsmouth, said: “After the U-turn this summer, it felt like the government finally understood that children can’t be left to go hungry during the holidays.
“But now we’re back in the same position of having to ask for help. Covid-19 isn’t going away, and even more families are struggling. Children need support during the holidays now more than ever.”
While 15-year-old Felix, who has eight siblings and lives in Norfolk, said: “For a really big family like mine, the holidays mean much more pressure on our parents – with me and my siblings at home there needs to be more meals, extra childcare, higher bills.
“For families fallen on hard times and for parents have lost their jobs because of Covid, the pressure to provide during the holidays must be overwhelming.”
A spokesman for the Westminster government said it had taken substantial action to make sure children and their families did not go hungry.
This included extending free school meals support to those eligible when schools were closed, extending welfare support by £9.3bn, funding councils to provide emergency assistance to families with food, essentials and meals, it said.
“We know it has been a challenging time for families which is why we have increased the safety net available to them with income protection schemes, mortgage holidays and support for renters.”