Today George Osborne will use his keynote speech to the Conservatives' autumn conference to underline how more than £10 billion of welfare cuts need to be found by 2016-17.
The Prime Minister set himself on a collision course with his Liberal Democrat deputy Nick Clegg as he forcefully ruled out a mansion tax on properties worth more than £2 million as well as benefits cuts for wealthy pensioners.
Mr Cameron said his party would "level" with the public about the need for another £16 billion of spending cuts in 2015-16.
"We have to find these spending reductions and if we want to avoid cuts in things like hospitals and schools, services that we all rely on, we have to look at things like the welfare budget," he told the BBC.
But he stressed the overall deficit reduction effort would involve the rich paying more, though he declined to say exactly where the extra money would come from.
"We are going to take further action to make sure the wealthiest people in our country pay their fair share towards deficit reduction," he declared.
With the Tories trailing in the polls and Labour's Ed Miliband enjoying a boost following his well-received One Nation speech last week, the PM and Chancellor kicked off conference with a raft of initiatives designed to regain control of the political agenda.
They included a promise to veto any proposal for "massive" increases in the EU budget; an extension of England's council-tax freeze for the third year in succession; and a cap of inflation plus 1% on rises in the UK's regulated rail fares.
The PM insisted he was looking at "working-age welfare" and would stand by his pre-election promise to protect universal benefits for pensioners such as bus passes and winter fuel payments, despite growing LibDem calls for them to be means-tested.
Mr Cameron stressed the LibDems' flagship mansion tax proposals were "not going to happen".
"If you work hard, you save, you buy yourself a house, you try to pay down the mortgage, you save and invest into that house, I don't want to be a country that comes after you every year with a massive great tax," said the Prime Minister.
Mr Osborne emphasised how the "wealthiest will bear the greatest share" of the cost of dealing with the deficit, but he too made clear there would be no mansion tax, or any other type of wealth tax that was levied annually on assets.
"Other countries have tried that and it hasn't worked. It's driven enterprise investment abroad," said the Chancellor.
Mr Cameron dodged questions about whether the economy was finally recovering from its double-dip recession and Mr Osborne refused to be drawn on whether he would have to abandon the Coalition's debt target, pointing out the Office for Budget Responsibility would produce more forecasts in December.
However, the Chancellor said he believed the "economy is healing" and the Government had the "right balance" on the pace of spending cuts.
Today in his keynote speech, Mr Osborne will underline how the Coalition is keen to support Britain's "strivers", arguing those who make the greatest effort deserve the greatest reward.
Meantime, in a joint article with Iain Duncan Smith, the Work and Pensions Secretary, the Chancellor will seek to dismiss suggestions of divisions over the Government's main welfare reform.
He said: "We are united in our determination to deliver Universal Credit, the most fundamental reform of our benefits system for a generation, on time and on budget."
Elsewhere in his speech, the Chancellor will also announce a £1 billion investment in science research with bids for the money made available across the whole of the UK.