England was worst hit by the increase in severe child poverty, with more than 1.5 million children now living in families earning 50% below the average income, evidence from Save The Children showed.
Wales has 96,000, Scotland 95,000 and Northern Ireland 43,000 children currently living in severe poverty, the charity added.
A spokesman for the charity said: "Measuring Severe Child Poverty in the UK reveals that 13% of the UK's children are now living in severe poverty and shows that efforts to reduce child poverty have not only stalled but have slid into reverse."
Evidence showed a sharp increase in severe poverty even before the recession, with an additional 260,000 children plunged into severe poverty during four years of UK economic boom before the recession hit in 2008.
Fergus Drake, director of UK programmes for the charity, said: "It's shocking that at a time when the UK was experiencing unprecedented levels of wealth the number of children living in severe poverty - we're talking about children going without a winter coat, a bed and other day-to-day essentials - actually increased.
"Measures introduced by the Government in the last two years have managed to prevent the numbers spiralling even higher but with unemployment expected to rise there is now a danger that severe child poverty will increase even further."
London has the biggest proportion of children living in severe poverty accounting for around one fifth of all children living in severe poverty in the UK - over 300,000 children.
The report also reveals that single parents and those out of work are those most likely to be living in severe poverty. Almost half of children in severe poverty were in single parent families and the same number in families claiming job seekers allowance (50%).
The recession is likely to have increased severe poverty by a further 100,000 children but rises in tax credits and benefits are expected to have bought the numbers back down to pre-recession figures, the researchers said.
The report, conducted by the New Policy Institute, also revealed Pakistani, Bangladeshi and black African children were around three times more likely to be in severe poverty than white children.
Department for Work and Pensions minister Helen Goodman said: "Over the last decade we have lifted half a million children out of relative poverty and also increased help substantially for the very poorest families to make sure they are better off.
"Families with children in the poorest fifth of the population are, on average, £5,000 better off as a result of personal tax and benefit changes.
"Without measures such as tax credits, employment help and the Sure Start programme, it is likely around two million more children would still be in poverty today.
"Significant investment made since Budget 2007 will lift a further 550,000 children out of poverty and we are helping to get parents into work by providing free childcare for three and four-year-olds.
"But there is still much more to do. We are determined to meet our ambitious goals and help break the cycle of deprivation, which is why we will enshrine in law our commitment to end child poverty by 2020."
Shadow work and pensions secretary Theresa May said: "These figures are a damning indictment of Labour's record.
"Despite targeting child poverty, Labour's approach was failing even before the recession. We can't go on like this.
"Labour's one dimensional approach with its focus on shifting people from just below the poverty line to just above it has failed to tackle the long-term causes of poverty, such as children growing up in work-less households, educational failure and family breakdown.
"We need a change to tackle these issues and address the causes of poverty.
"A Conservative government would give specialist help to get people into work through our Work Programme to get Britain working, would bring in a pupil premium which would target more help at poorer pupils and would remove the couple penalty in the tax credit system which would lift 300,000 children out of poverty."
Liberal Democrat work and pensions spokesman Steve Webb said that Government policies for tackling poverty had failed while there were "gaping holes" in the Tories' plans.
"Labour has failed to tackle child poverty with its complicated tax and benefit tricks. Ministers have run out of ideas," he said.
"The Liberal Democrats will invest more in education to give every child a fair start and break the link between poverty and low grades."
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