The new coalition governments emergency Budget announced in June has hit the poorest families hardest, a leading economic think tank says.
The Institute for Fiscal Studies IFS said the measures announced in the Budget were regressive.
Its analysis suggests the poorest households are set to lose the most as a precentage of net income due to benefit cuts announced in the Budget.
The Treasury said it did not accept the selective findings of the IFS.
Housing costsThe IFS had already challenged the governments claim that the Budget was progressive.
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End Quote Yvette Cooper Shadow work and pensions secretaryThe idea that the poorest families with children should end up being hit hardest is appalling�
Its analysis suggests that cuts to areas such as housing benefit and disability allowance would hit the poorest families to the tune of �422 between the Budget and April 2014.
This means that only the richest 10% of households lost more in cash terms from the budget, than those in the bottom 10%.
The report also questioned the governments decision to use the Consumer Price Index CPI instead of the Retail Price Index RPI when calculating certain benefits.
It said that more than three-quarters of benefit claimants were affected by increases in housing costs, which are included in the RPI.
Selective analysisThe shadow work and pensions secretary Yvette Cooper accused the government of carrying out a shocking and unfair attack on children and families.
The idea that the poorest families with children should end up being hit hardest is appalling and gives lie to [Chancellor] George Osbornes claim it was a progressive budget, she said.
A spokesman for the Treasury said: The government does not accept the IFS analysis.
It is selective, ignoring the pro-growth and employment effects of Budget measures - such as helping households move from benefits into work, and reductions in corporation tax.