BBC: 'Further cuts will affect programmes'
The BBC is preparing to announce how it will save more money, having already clawed back more than £1bn a year through cost-cutting measures.
A new report will say the corporation needs to save an extra £400 million a year by 2017.
However, it warns that further cuts will have an adverse impact on programmes and services.
The corporation has already announced the intended closure of TV channel BBC Three, which will move online.
Some press reports have suggested that BBC Four could follow suit, but the BBC's director of strategy, James Purnell, refused to speculate on its future during an interview on Radio 4's Today programme.
"We don't want to close BBC Four," he said.
"What we're doing is making efficiency savings, and what we've published today is a document that shows that over the last few years we've saved about £1.1bn of our costs.
"By the end of this charter period, in two years time, that'll be £1.5bn - that's nearly half of the costs that we control at the BBC."
The BBC's report comes as it prepares to negotiate with the government for the renewal of its Royal Charter in 2016.
Conservative politicians have hinted the corporation could face further budget cuts, with culture secretary Sajid Javid calling the £145.50 annual licence fee a "large amount [that] needs to be looked at".
The BBC's report emphasises it cannot repeat previous one-off cost-cutting measures, such as the sale of London's Television Centre, which raised £200m.
It has shed more than 1,000 staff and reduced the pay packets of its star performers by £22m since 2008.
The report stresses that most of the cuts have been behind-the-scenes, with more than 90% of the licence fee now spent on content.
"It's vital that as much of the licence fee as possible goes straight to the programmes and services audiences love," said BBC finance chief Anne Bulford, launching the document.
"This report shows we've made great strides in becoming more efficient. We're doing far more for less."
However, the broadcaster has also come under fire for wasting money, particularly through the failure of its Digital Media Initiative, which was axed at a cost of £100 million last year.
The National Audit Office also criticised the BBC for paying £25m to 150 outgoing senior executives between 2009 and 2012 - some £2m more than their contracts stipulated.
"Every organisation is wasteful," said Mr Purnell, "but the fact that we've saved 5% a year for the last 20 years has actually been a huge transformation in our productivity.
"The licence fee has been pretty much flat in real terms, and yet we've given people new services like BBC Three, BBC Four and the iPlayer. That's been a huge improvement in the value people get, without them having to pay any more."