Families with children will be hardest hit by coalition spending cuts, Ed Miliband has warned.
The Labour leader stepped up his attack on the deficit reduction plans as he sought to capitalise on momentum from the Barnsley by-election.
Research commissioned by the party from Landman Economics suggests that on average, couples with children stand to lose around £2,500 worth of public services annually. That is over £1,000 more than those without children, according to the calculations.
Families where the main breadwinner is aged 25-29 will lose the equivalent of 12% of their income if they have children - and just 4% if not.
Mr Miliband told a conference of Labour councillors in London: "We have always assumed that our children, the next generation, would do better than us. Not just the well-off, but the vast majority of people used to expect that their children will do better than them...
"But there is now a real fear that the British promise will be broken and the next generation will find it harder to get on than the last."
Mr Miliband also insisted that this week's by-election victory showed Labour was "on the move", while the Liberal Democrats were "humiliated".
"I think it's becoming clear to voters that, while there might - still - be three main political parties, there are only two directions for the future of our country," he said. "There are some decent Liberal Democrats out there who hate what their leadership is doing.
"But at a local and national level, voters understand they are powerless to stop Nick Clegg and the Liberal Democrat leadership from signing up for some truly terrible decisions."
He appealed to Labour activists to fight May's local elections as if they were a general election, urging them to dispel the "myth" that the coalition needed to cut spending as quickly as it was, saying: "We know where the responsibility for cuts lie.They lie firmly with this Conservative-led government, and we should never shy away from making that clear."
