More than 350,000 children could lose their free school meals under the government's planned welfare reforms, a charity has warned.
An analysis by the Children's Society found more than 1.2m youngsters living in poverty are currently missing out on the dinners which are linked to low-income benefits.
In a report, it said ministers were considering a new income cap for eligible families which could leave more than 100,000 households worse off.
The government is considering a new streamlined system of universal credit to replace the current array of benefits and tax credits, raising fears that hundreds of thousands of families could be left with lower entitlements.
The charity said such moves risked creating a "cliff edge".
If an earnings threshold of £7,500 was introduced for entitlement to free school meals, 120,000 families in England - with around 350,000 school age children - would lose out, it said.
Parents would consequently have to slash their working hours or take a pay cut to keep their benefits.
According to the charity's Fair and Square report, 2.2 million English schoolchildren are living below the poverty line.
More than half of these youngsters are not receiving free school meals while 700,000 are not entitled to the dinners, it revealed.
Elaine Hindal, director of the Children's Society's Campaign for Childhood, condemned the "policy failure" but said the government has an opportunity to increase the availability of free school meals to all low-income working families.
"We have shown that there are literally hundreds of thousands of children living below the poverty line who aren't getting a free school meal," she said.
"There is no reasonable defence for this policy failure."
The Children's Society is calling for all children living in poverty in England to be entitled to a free meal by October.
Its report follows a study released earlier this month which revealed young children in England were being served "very small" school dinners and given limited choice despite paying more.
The survey, conducted by the Association of Teachers and Lecturers, showed almost a third of teachers do not believe that school meals are value for money.
According to recent figures from the School Food Trust, 79.8% of pupils registered for free school meals in primary schools were taking up their meals, compared with 79.3% in 2009/10.
In secondary schools, 69.3% of those registered took up the dinners, compared with 68.4% in 2009/10.
An estimated 1,055,000 free meals were being served every day in 2010/11, the trust said.
Children's minister Sarah Teather said: "We remain totally committed to continuing to provide free school meals (FSM) to children from the poorest families.
"We are reforming welfare to get more people into jobs as that is the surest way of cutting poverty.
"The reforms mean we will have to think hard about the best way to decide who is eligible for FSM so they continue to be targeted at those who need them the most.
"No plans have yet been set and we will be consulting later this year about the best way forward."
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