Anti-poverty campaigners have voiced deep concern over Government plans to ditch legal requirements to lift children out of relative poverty.
Work and Pensions Secretary Iain Duncan Smith announced plans to replace Labour's Child Poverty Act, which established a duty for governments to eradicate the problem by 2020, with new legislation which will instead require ministers to report regularly on measures affecting a child's life chances.
In a statement to MPs, Mr Duncan Smith said he was scrapping the official measures and targets used in the 2010 Act, which defines a child as being in poverty if it is in a household with less than 60% of the national median average income.
The measure was deeply flawed because it meant that child poverty was dependent on unrelated factors which had no effect on real children's lives, he said. Child poverty could be officially reduced by a slump in the economy or increased by a hike in state pensions, he pointed out.
Labour denounced the move as "the death knell of compassionate conservatism".
Acting shadow work and pensions secretary Stephen Timms said: "Their manifesto said they would work to reduce child poverty, instead they have decided to change the definition."
But Mr Duncan Smith insisted: "Eradicating child poverty is an absolute priority for this Government, and I have consistently argued that it is not enough to tackle the symptoms without also tackling the underlying causes.
"The measures announced today are the foundation of a new, comprehensive way of addressing poverty and reflect our conviction that work is the best route out of poverty.
"Our new approach will drive effective Government action by focusing attention on making meaningful change to children's life chances."
The new law will introduce measures on educational attainment and numbers of children in workless households, while ministers will also be required to report on levels of family breakdown, problem debt and drug and alcohol addiction.
The long-expected change came after a report from the four UK children's commissioners warned child poverty rates across the UK were "unacceptably high".
The Child Poverty Action Group (CPAG) accused the Government of "turning its back on poor children" ahead of further cuts to welfare expected to be announced in next week's Budget.
CPAG chief executive Alison Garnham said: "Today's statement isn't about strengthening efforts to end child poverty but about burying the failure of the Government's child poverty approach. And with more cuts coming down the line, child poverty is set to rise.
"Two thirds of poor children are in working families - it's unclear whether these children will be counted as poor in the future ... A child poverty strategy which excludes income isn't a child poverty strategy."
Barnado's expressed "deep concern" about the move and urged the Government not to scrap its legal commitment to tackle child poverty. Chief executive Javed Khan said: "With every day that passes more families tell Barnardo's they face debt, hunger and homelessness because low wages and benefits changes have left them unable to pay for the basics. Tinkering with the way we measure poverty will only mask, not relieve, the daily misery of their lives."
Peter Grigg, director of external affairs at The Children's Society, said: "Today the Government has decided to break its promise to end child poverty by 2020 ... Income is at the heart of child poverty. Ignoring it will only mean more ineffective policies that continue to fail. This will condemn increasing numbers of children to live below the breadline, which is a national disgrace."
The announcement comes after a review of the relative poverty measure commissioned by Mr Duncan Smith in 2013. He told MPs that the measure resulted in "unintended consequences" as action was focused on lifting children above the 60% line rather than on tackling the root causes of their disadvantage.
"Governments will no longer just focus on moving families above a poverty line, instead we want to focus on making a meaningful change to children's lives by extending opportunity for all so both they and their children can escape from the cycle of poverty and improve their life chances," he said.
"This process marks a shift, I hope, from solely measuring inputs of expenditure to measuring the outcomes of children-focused policy."
Mr Timms said: "David Cameron's Government is trying to make child poverty go away by pretending that if you don't measure it, it doesn't exist.
"Ministers should be tackling low pay, boosting productivity and raising skill levels to cut child poverty, rather than threatening the tax credits that millions of working families rely on. It's time for this Government to make work pay, rather than making working families pay."
But the Labour chairman of the House of Commons Work and Pensions Committee, Frank Field, said: "This is a really welcome start. But we mustn't flit around with general aspirations about educational attainment when we know life chances are determined before children enter school.
"So the measure therefore must look at whether we are equalising life opportunities for the poorest children before they reach school, and that definition will then drive policy to achieve those objectives."
Mr Duncan Smith also announced that the Social Mobility and Child Poverty Commission, chaired by Labour's former minister Alan Milburn, is to be renamed the Social Mobility Commission, with a remit to ensure independent scrutiny and advocacy of ways to boost people's life prospects.