Chancellor George Osborne should announce further cuts to the welfare budget and the civil service, former Cabinet minister Liam Fox said as he indicated he would like to return to frontline politics.
Dr Fox, a standard-bearer for the Tory right, called for deeper reductions in public spending and tax cuts for businesses as he identified economic growth as the key factor if the Tories are to win the next election.
"We need to get a firmer grip on spending. One of the biggest rises in our budget is the interest we are paying on our debt. That has risen from just over £40 billion, it will rise to almost £60 billion by the next general election," he told Sky News' Murnaghan programme
"That means that we are paying more in debt interest than we are spending on defence and overseas aid and the foreign office all combined."
He said Mr Osborne should target the welfare budget and the size of Whitehall as areas for spending cuts.But he also called for a package of tax cuts to boost business.
"Cutting taxes on business I think is key to get more people into work, I personally would like to see capital gains tax taken down to get more activity into the economy. We need to be creative: if we are creative we get growth, if we get growth we get re-election.
Fox acknowledged there had been "muttering" about David Cameron's leadership but insisted the Prime Minister had silenced his critics over Europe.
He praised Mr Cameron's announcement that a Tory government would offer an in/out referendum on membership of the European Union, which he claimed had blunted the threat to the Tories posed by the UK Independence Party (Ukip).
"What would be the point in a general election of voting for a party like Ukip ... when the Conservatives will promise and deliver a referendum if we are elected, and voting for a party like Ukip can only increase the chance of Labour being re-elected and they will deny the voters a choice," he said.
Asked if he would take a post in the government if Mr Cameron offered it, Dr Fox said anyone offered the chance to serve their country "ought to say yes".
Questions about Mr Cameron's leadership have been asked in recent weeks after reports that backbencher Adam Afriyie was being touted as a potential successor.
Asked on Sky News' Murnaghan programme if Mr Afriyie was a "stalking horse" acting as cover for his own leadership challenge, the former Cabinet minister said: "I've been in Parliament for nearly 21 years and I can never remember a time in all 21 years when there wasn't muttering going on about whoever was the party leader at the time or prime minister at the time.
"Party leaders have to get over that and go ahead and do what they believe to be correct. The Prime Minister got a great victory for the UK at the EU summit this week, which of course all those defeatists said would not be possible.
"He went in, negotiated hard, showed considerable diplomatic skill and got a great outcome for the United Kingdom."
Dr Fox quit the government over his controversial relationship with self-styled adviser Adam Werritty but indicated he would accept an offer of a return to the ministerial ranks from Mr Cameron.
"That's not a question for me, that's a question for the Prime Minister and I'm sure he will have his view on that.
"If anyone was asked by a prime minister if you are willing to serve your country I think they ought to say yes."