Why the political split over measuring child poverty?
The government was legally required to update its anti-poverty strategy to demonstrate what it was doing to meet the terms of the 2010 Child Poverty Act.
But Iain Duncan Smith wanted to be more ambitious.
He has long denounced the income-based measurements of relative poverty which he inherited from Labour.
He sent the idea of a broader measure of poverty out to consultation in 2012.
He picked up support from some leading charities.
That's in part because children are said to be in poverty if they live in households which have an income that's less than 60% of the national average.
So when incomes in the economy as a whole fail to keep pace with prices, it could appear that some families are less poor simply because their low income is a tad closer to a lower average and not because they are a penny better off.
Iain Duncan Smith wanted a more sophisticated measure - taking in to account whether children have access to a good education, a decent home, and a stable family. He reached a deal with his Lib Dem colleagues.
But after a series of meetings between the Treasury and the Department for Work and Pensions he has been compelled to agree with the chancellor that it will take even more time to get new measurements right.
The Treasury are sticking to the line that they haven't blocked a new measurement - but they certainly have sent it on a long diversion.
There were some fears in government that changing the definition could look like an attempt to massage the figures - after all, just as falling incomes appear to lift people out of relative property, when the economy recovers and average incomes improve, then more people could appear to be relatively poor.
So changing the definition, critics would argue, could make it easier for the government to meet the target of eradicating child poverty by 2020.
But the Treasury were worried about the opposite problem.
Could changing the definition make it more difficult to be seen to be making progress and could it be too costly?
In the end, no agreement between the Treasury and Department for Work and Pensions could be reached on how much resources would have to be devoted to meeting a new broader measure - and the consultation continues.