George Osborne told the BBC's Today programme earlier this morning that he does not want to "let Whitehall off the hook" when it comes to making savings in the spending review.
My central assumption in this spending review is that this is money I am now looking for which is coming out of Whitehall departments, that we have already found billions of pounds of welfare savings this year and we have got to make sure that Whitehall is not let off the hook, that there are still substantial savings - better value for money we can get for taxpayers' money out of the machinery of government.
George Osborne has told BBC's Today programme that he is "in effect" ruling out further cuts to welfare in the Spending Review.
We've just got seven departments to agree to substantial savings. They've accepted cuts of anywhere between eight and 10 percent... It's a difficult decision, I'm not hiding that from anyone - but it's necessary.
But a spokeswoman for Mr Duncan Smith said: "Iain has not had any special discussions about protecting the defence or security budgets. These measures were on the table at the time of the Autumn Statement."
Chancellor George Osborne has said that seven government departments have provisionally agreed to cuts of up to 10% for 2015 to help make savings of £11.5bn.
Speaking to ITV's Daybreak, Mr Osborne said: "This will enable us to get this deficit down and also, crucially, spend money where I think the public want it spent, which is on things like the NHS and on the kind of infrastructure".