Iain Duncan Smith will seek to reassure critics that he is committed to ending child poverty but insist that "meaningful and accurate" measures must replace "arbitrary" household income targets.

The Work and Pensions Secretary will launch a consultation on controversial plans to move away from the poverty indicator introduced by Labour, which defines it as those children living in households with less than 60% of the median income.

Campaigners are concerned that the Government is trying to duck commitments to ending child poverty by 2020, but Mr Duncan Smith will say that new measures are needed to take into account issues like worklessness, debt and family breakdown which underlie child poverty.

"A fixation on relative income, on moving people over an arbitrary line, does little to identify those most in need and entrenched in disadvantage, nor to transform their lives," Mr Duncan Smith will say at Clyde Children's Centre in Deptford, south east London.

"For families across the UK, who are income poor, but more than that, whose lives are blighted by worklessness, educational failure, family breakdown, problem debt and poor health, as well as other problems, giving them an extra pound - say through increased benefits - will not address the reason they find themselves in difficulty in the first place."

The Conservative Cabinet minister will use the example that, according to latest figures, 300,000 children have been moved out of relative poverty on the current measure. But that was due to the median income nationally falling rather than to any improvement in circumstances for those children.

Mr Duncan Smith will accuse Labour of leaving the root causes of poverty "unchecked" and failing to "break the cycle of disadvantage", despite spending £171 billion on tax credits. He will say that no statistics can entirely reflect a child's life, but insist a better indicator was possible than the current measure.

Barnardo's chief executive Anne Marie Carrie said the Government should continue to measure income and not lose sight of the action needed to improve children's lives. She said: "We know that children growing up in low income households are more likely to suffer from chronic illness, do less well in education and struggle to find work on leaving school, which is why Barnardo's urges the Government to keep measuring income but also to help families climb their way up and out of the poverty trap by helping them to manage debt, understand what benefits they are entitled to and manage the impact of rising fuel prices."

Schools minister David Laws told BBC Radio 4's Today programme that to get policy right, "you have to measure child poverty in a sensible way".

Mr Laws said the aim needed to be about taking people out of poverty in the long term and "not just maintaining them on means-tested benefits".