Liberal Democrat leader Charles Kennedy has warned of a "continuing widening of the gap between rich and poor".
Mr Kennedy said inequality was worse than under Margaret Thatcher
In his New Year message, he accused Labour of "tinkering" with policy and "giving way" to pressure to reintroduce selective secondary schools.
Labour said it was the party that had lifted two million children and pensioners out of poverty.
Mr Kennedy also told the BBC he intends to fight the next election, despite reports of no-confidence vote plans.
'No leadership election'
A senior MP has reportedly threatened a poll within 14 days if Mr Kennedy does not stand aside.
But the Lib Dem leader said: "I was very gratified and very heartened by the overwhelming expression of support I got from my parliamentary colleagues.
"It's quite clear from all that's come in since the end of the... session last week that there is no mood whatsoever among the members of the Liberal Democrats for a leadership election."
In his message, Mr Kennedy said: "Unfairness divides our society. Inequality is worse than under Margaret Thatcher."
He called the tax system "unfair", with "life chances and opportunities" reduced.
Mr Kennedy added: "Those born into poor circumstances are more likely to be trapped under Labour.
"It is the sad fact that a party once dedicated to the advancement of the under-privileged has presided over an ever-growing divide."
He also criticised Tory leader David Cameron, who has called for Lib Dems to defect to his party.
Mr Cameron, who was elected as Tory leader at the beginning of December, was "the newest kid on the block" and "reaping the rewards for being fresh", Mr Kennedy said.
He added: "David Cameron is a Conservative at heart, not a liberal.
"But what I do also detect is a shifting of the political tectonic plates - a sense that change is coming.
"And when this government falls, as one day it must, I believe it is the Liberal Democrats, the genuine bearers of the liberal and democratic flame in our country, who will be most in touch with how the majority want us to respond to such inequalities and unfairness."
Mr Kennedy said local government elections next May would be a chance for the Lib Dems to make gains.
A Labour Party spokesman said the Liberal Democrats had opposed key measures central to ending inequalities, such as the pension credit, increases in the minimum wage and the New Deal.
"The Lib Dems can have no credibility when they have dumped their tax commitments from the last election but none of their spending commitments," he added.