Government departments could be in line for further cuts to their spending at next month's Budget, George Osborne has said.
The chancellor has vowed to achieve a £10bn surplus on the UK's budget by 2020, and unprotected government departments drew up plans for their own contributions towards that aim at November's Spending review, with cuts across those departments averaging 18% on current levels.
But, speaking to the BBC, Osborne said slower-than-expected growth and global economic uncertainty meant departments may need to make "further efficiencies".
IFS on the Spending Review: “Lucky” Osborne has eased the squeeze – but chancellor may have to revisit cuts plan
Spending Review 2015: The departmental settlements
"We may need to undertake further reductions in spending because this country can only afford what it can afford and we will address that in the Budget," he said. "We've just had new figures that show the economy is smaller than we thought in Britain, and we also know that global risks are growing and Britain is not immune to those things."
Osborne's comments came as the International Monetary Fund warned of "uncertainty and increasing downside pressures" – including the slowdown in China and volatility in commodity prices – which it said "could put at risk the global economic recovery".
Figures published by the Office for National Statistics last week showed that the UK economy grew at just 0.5% in the latest quarter.
While Osborne said the UK was doing "better than most countries", he argued that further spending cuts could help to shore up the public finances
He added: "We'll set it out if we need to, how we'll reduce spending, but the first place I look to is further efficiencies in government. There are always ways to make government better, always ways to make sure that the taxes of people are better spent.
"All I'm talking about is going back to government budgets and saying where we can find that extra saving, that extra efficiency, that extra improvement in the public service that might release some money."
At November's Spending Review, Osborne used revised economic forecasts from the Office for Budget Responsibility – showing lower-than-expected debt interest payments and higher tax revenues – to ease some of the planned squeeze on departmental resource budgets.
But the independent Institute for Fiscal Studies said there was a "50-50 shot" that Osborne would have to "either to revisit these spending decisions, raise taxes, or abandon" his surplus target should the economic picture change over the next four years. The chancellor's room for manoeuvre in achieving that aim is also limited by Conservative manifesto pledges not to raise income tax, VAT or national insurance.
Shadow chancellor John McDonnell said the admission that further cuts could be needed showed that the government's economic plans were "built on sand".
"Far from paying our way, Osborne's short-term economics means Britain is deeper and deeper in hock to the rest of the world," the Labour frontbencher said.
"If the Bankers' Chancellor had been doing his job properly he would be collecting taxes from Google and other tax-dodgers. Instead he is threatening the British people with paying an even higher price for his own failures."