David Cameron has made it clear he will resist pressure from within his Cabinet and on the Conservative backbenches to ditch the protection from cuts which he has granted to the NHS, schools and overseas aid.
Little more than a week ahead of Chancellor George Osborne's March 20 Budget, critics of the PM's approach have set their sights on the so-called "ring-fence" for favoured priorities, arguing that it is forcing departments like justice, transport and the Home Office to bear the brunt of cost-cutting.
In a speech calculated to appeal to the Tory right, former defence secretary Liam Fox questioned whether shielding particular areas "makes sense in a period of prolonged austerity".
And Business Secretary Vince Cable warned that continuing the ring-fence - which covers budgets accounting for 60% or more of expected increases in government expenditure - risks distorting public spending.
"It means that all future pressures then come on things like the Army, the police, local government, skills and universities. So you get a very unbalanced approach to public spending," Mr Cable told the BBC Radio 4 Today programme.
However, Mr Cameron left no doubt about his commitment to maintaining health spending, telling an audience in Milton Keynes: "There is one piece of advice that I won't take, and that is the piece of advice that says you ought to cut the National Health Service budget.
"We made a very clear promise before the last election that yes, we were going to have to take difficult decisions, yes, we were going to have to make some very difficult and painful cuts, but we wouldn't cut the NHS budget."
Downing Street said that there was also no change in the PM's policy of protecting schools and aid from cuts until at least 2015/16, as well as ensuring a 1% annual real-terms rise in defence equipment spending from 2015.
In a high-profile speech in London, Dr Fox called for a freeze in all public spending lasting up to five years, to pay down the UK's national deficit and fund tax cuts.
Dr Fox said that a three-year public spending freeze would save the Government £70.4 billion a year. Extending the freeze over five years would save a total £345 billion, he said, adding: "As a Conservative, such a commitment doesn't scare me."
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