Labour leader Ed Miliband has said his party will be the "people's voice in tough times", as he attacked spending cuts in his New Year message.
Mr Miliband said the scale of cuts was "born of political choice by those in power, not necessity".
Plans to eliminate the structural financial deficit by 2015 were "irresponsible", he added.
Lib Dem president Tim Farron said "hard-working families" had been hit by Labour's failure to protect them.
Mr Miliband, who succeeded Gordon Brown when he narrowly beat his brother David to the party leadership in September, also promised to "change Labour" and try to rebuild trust following its election defeat.
In his New Year message he said 2011 would be a "year of consequences for Britain. Consequences that will be felt by hard-working families across the country".
He repeated his criticisms that the government's deficit reduction plan was being done at an "irresponsible pace and scale".
In October Chancellor George Osborne outlined plans for an £81bn package of public sector spending cuts, in an effort to reduce the UK's record budget deficit. He argued it would restore "sanity to our public finances and stability to our economy".
But Mr Miliband said the cuts were "born of political choice" - Labour argues it is an "ideological objective" of the Conservatives to cut the size of the state.
The Labour leader said he believed cuts were being done at an "irresponsible pace and scale" and called for a "proper economic strategy rather than an economic policy reduced only to deficit reduction".
He repeated his argument that Labour would have made cuts - but that the size and pace would have been different.
He said young people were worried about the impact of the decision to increase the cap on university tuition fees in England from £3,290 per year to a maximum of £9,000 and to axe the educational maintenance allowance - policies which prompted large protests across the country.
"In 2011 many people will wonder what they can do. Some will ask whether there really is an alternative to this scale of cuts. Still more will shrug their shoulders at casually broken promises and conclude politicians are indeed all the same.
"Labour's challenge and duty in 2011 is to be people's voice in tough times and show that these are changes born of political choice by those in power, not necessity.
"And we will take the next steps on the journey to win people's trust that we offer a better, more optimistic future for Britain."
'Verge of bankruptcy'
Labour had "lost touch and lost trust" in government, he said, and "needed to change to be the party that Britain needs".
"We must change our party so that it becomes a genuine community force in every part of the country."
The coalition has accused Labour of economic mismanagement and says Labour were planning huge spending cuts of their own before the election but were not being prepared to spell out where they would fall.
Liberal Democrat president Tim Farron said: "If 2011 is the year of consequences, they are the consequences of Labour leaving us on the verge of bankruptcy.
"Ed Miliband has called for a 'proper economic strategy' - but the last one, cooked up with Gordon Brown while Ed was in the Treasury, didn't really work out so well."
He added: "Hard-working families are suffering because Labour failed to protect them in boom and bust."