George Osborne's emergency Budget hit the poorest hardest, a leading economic think-tank has said.
The Institute for Fiscal Studies (IFS) concluded that the biggest losers from the measures announced by the Chancellor in June were low income households with children.
The report was seized on by Labour, with shadow work and pensions secretary Yvette Cooper accusing the Government of carrying out a "shocking and unfair attack on children and families".
But the Treasury said it "does not accept" the IFS analysis, claiming the report was selective in what Budget measures it had included.
The IFS study found that the poorest six tenths of households lost more in cash terms as a result of the Budget's changes than wealthier households in all but the richest 10 per cent.
"Our analysis shows that the overall effect of the new reforms announced in the June 2010 Budget is regressive, whereas the tax and benefit reforms announced by the previous government for introduction between June 2010 and April 2014 are progressive", the report said.
"Low-income households of working age lose the most from the June 2010 Budget reforms because of the cuts to welfare spending.
"Those who lose the least are households of working age without children in the upper half of the income distribution.
"This is because they do not lose out from cuts in welfare spending and are the biggest beneficiaries from the increase in the income tax personal allowance."
A Treasury spokesman 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.
"It is essential that policy is informed by transparent analysis: That's why we stand full-square behind our Budget analysis which is based on what can accurately and completely be measured.
"Not taking action would have been regressive - burdening current and future taxpayers with the ever rising cost of economic failure."
