Nick Clegg has opened a divide within the coalition Government by calling for the means-testing of a range of benefits for pensioners.
The Government is committed to preserving the universal benefits - such as winter fuel allowance and free bus travel, prescriptions and TV licences - until 2015, and Prime Minister David Cameron has so far resisted pressure from Tory backbenchers to signal he will cut them after the general election.
But the Deputy Prime Minister broke ranks to make clear that Liberal Democrats will "look again" at universal pensioner benefits, arguing that welfare cash "should not be paid to those who do not need it".
"I just don't think it's justifiable, when so many people are tightening their belts, to say multi-millionaire pensioners still receive universal benefits across the board," said the Lib Dem leader.
Asked if Mr Cameron backed Mr Clegg on the issue, the PM's spokesman responded: "The Prime Minister made a commitment to protect those benefits and he believes in keeping his promises."
But there was dissent on the Tory backbenches, as Broxbourne MP Charles Walker said Mr Cameron should be ready to make the universal benefits taxable as income before the election, to show that the older generation are bearing their share of the burden of reducing the deficit.
Mr Walker told BBC Radio 4's PM programme that working people were "pretty sore" at seeing their child benefit and other support withdrawn or reduced, while pensioners' payments are protected.
In a keynote speech marking his fifth anniversary as Lib Dem leader, Mr Clegg mounted a vigorous defence of the coalition's welfare reforms, insisting the Government had an "absolute duty" to ensure the system was fair to all.
While acknowledging the changes had at times been "painful and controversial", he argued that the Liberal Democrats had ensured they were firmly anchored in the political centre ground. When the Conservatives proposed benefit cuts of £10 billion in the Autumn Statement, the Lib Dems had acted as a moderating force, ensuring they were held to £3.8 billion, he said.
"When two-thirds of people think the benefits system is too generous and discourages work then it has to be changed, or we risk a total collapse in public support for welfare existing at all," Mr Clegg told the CentreForum thinktank.