'£580' cost of benefit change
Tax and benefit changes will cost the average family with children £580 from April, according to the Institute for Fiscal Studies (IFS).
The independent think-tank's analysis will be seized on by Labour leader Ed Miliband, who will today accuse the coalition Government of another "squeeze on the squeezed middle".
In a letter to shadow Treasury secretary Rachel Reeves, the IFS reported that households with children would be £580.03 worse off as a result of tax and benefit changes to be implemented for the 2012/13 financial year.
Of that, £32.55 was the result of changes announced in the 2011 Autumn Statement - including to child tax credit, working tax credit, pension credit and fuel duty - which will make pensioner households £48.35 better off and benefit working-age childless households by £73.34.
In a speech to the Welsh Labour conference in Cardiff today, Mr Miliband will accuse the coalition of failing to assist families with the rising cost of living.
"On current forecasts, the average worker will be earning the same in three years' time as they were ten years ago, but the weekly shop costs more, it costs a lot more to keep the house warm and we have a government that doesn't believe that its job is to stand up for ordinary people against powerful vested interests.
"What is their answer to the crisis of living standards? Cutting taxes for the banks while they raise taxes on ordinary families, higher VAT, cuts to tax credits.
"As the IFS have confirmed today, this April the Government is hitting an average family with children for £580. Choosing to squeeze the squeezed middle yet again."
Mr Miliband will also use his speech to defend the Union from the attempts of Scottish nationalists to break up the United Kingdom.
He will urge the Welsh to help the campaign against Scottish independence, insisting it affects Wales as much as the rest of Britain.
"I believe devolution has strengthened the United Kingdom, not weakened it, and we all have a duty, from every part of the United Kingdom, to fight for our United Kingdom," he will say.
"This is as much an issue for the people of Wales as for the rest of the UK.
"Why? Because we are stronger economically together and weaker apart, but also because we know something else - we are linked together by a common history, family ties, and shared bonds, the history of our islands is a history we built together.
"The family in Wales cares about the children in poverty in England, they care about the pensioners in Scotland.
"We want to change our country not just for people in one part of it, but for people in the whole of it: our United Kingdom."