Liberal Democrat leader Nick Clegg has denied plans to "soak the rich" but suggested it was right to consider ending pension tax breaks for the wealthy.
Mr Clegg said there was a "legitimate debate" to be had about poorer taxpayers footing the bill for pension relief for the rich.
He also insisted that the Lib Dems were winning public support for their plan to impose a "mansion tax" on large properties, as the party sought to draw dividing lines with the Conservatives over how to balance the nation's books.
On Sunday, in a thinly-veiled attack on Chancellor George Osborne, he dismissed as "wild" Tory calls for £10 billion to be slashed from the welfare bill after 2015.
Mr Clegg acknowledged that further austerity would be needed, but said: "Whoever is in government after the next general election will have to embark upon new belt-tightening - more savings, more cuts. That is just a reality, an inescapable one.
"What I am saying is, that being the case, we have got to decide now as a matter of principle how we approach that difficult task. My view is that you start at the top and then you work down, you don't start at the bottom and ask the poorest to make the greatest contributions and then work up.
"There are numerous ways that you can do that, we have always advocated a change to the tax system applied to very high-value property. It cannot be right that an oligarch in a £4 million palace in central London pays the same council tax as someone in a four-bedroom family home. That's not right, that's why we want to change it. We haven't yet won that argument but it's an argument that we are going to continue to make every single day."
The Lib Dems have pressed the case for a mansion tax since entering the coalition in 2010, but have so far faced resistance from their Conservative senior partners. The Liberal Democrat manifesto at the 2010 election proposed a £5.45 billion saving from ending higher rate pensions relief.
Mr Clegg acknowledged that there would need to be more welfare reform, but insisted it would not be right to make benefits claimants pay for the excesses of bankers.
He said: "I don't think you can realistically assume that as belt-tightening continues that somehow welfare, which in total constitutes about a third of public spending, can somehow be immune."