Liberal Democrat leader Nick Clegg has insisted on "savage" spending cuts at the next election.
By Alex Stevenson
His comments come as his party revealed documents casting the validity of Conservative plans into doubt.
As his party's last autumn conference before the general election gets underway, Mr Clegg rounded off a week of debate about spending cuts by issuing his own stark assessment of Britain's finances.
He could save £1.5 billion a year by removing tax credits paid to the middle classes, including child benefits.
A long-term freeze on public sector pay could bring government spending down further, he proposed.
"I find it odd that people on multi-million pay packages from the city get child benefit. That's patently silly and patently unfair," he told the Guardian newspaper.
"In some cases we will be quite bold, or even savage, on current spending, precisely to be able to retain spending where you need it in areas where the economy is weak in infrastructure."
Treasury documents obtained by freedom of information requests revealed Tory policy proposals would lead to an extra £53 billion of unfunded public spending, Lib Dem Treasury spokesman Matthew Oakeshott said.
"The Tories try to talk tough on spending cuts, but in reality they haven't a clue. With over £50 billion of uncosted spending commitments, they are clearly not fit for government," Lord Oakeshott said.
"The Tories claim Britain is bankrupt. It's not - yet - but it soon would be with George Osborne in No 11 Downing St."
Mr Clegg was bullish about his party's prospects. He highlighted success on the Gurkhas, constitutional reform and Trident, and pointed out the party polled 28 per cent in June's local elections.
"I do not believe that that is flatlining," says Clegg.
Perhaps signalling a willingness to focus on Labour seats in the general election, he focused his criticisms on the governing party.
"They need to rethink themselves a bit as well and understand that I'm not offering them just another reheated version of big state socialism, but the reverse. It's based on a criticism of big state socialism."
He said he would not immediately scrap tuition fees for higher education students and revealed he would not hold a referendum on electoral reform on the same day as a general election.
"I am filled with despair, as a lifelong electoral reformer, at the spectacle of a Labour government, having failed to do anything about reform for 12 years, now from a position of desperation putting the issue to the British people on the very day the British people are going to give them a big kicking in the general election.
"I guarantee is that it will discredit the case for electoral reform for a generation."