"Lower saving can only support growth in spending for so long," said Samuel Tombs, a U.K. economist at Capital Economics. "For now, the economy's growth spurt seems to be exacerbating existing imbalances in the economy, rather than helping them to heal."
David Kern, chief economist at the British Chambers of Commerce, said the government needs to think of new ways to boost exports to foster a rebalancing.
Prime Minister David Cameron has made trade a centerpiece of his foreign policy, although economists say British exports are likely to remain weak as long as demand in the biggest market for U.K. goods and services—the euro zone—remains subdued.
Friday's data did include some welcome news for Mr. Cameron and Chancellor of the Exchequer George Osborne.
Business investment grew 2% between the second and third quarters, and figures suggest the economy grew faster in 2012 than earlier estimates. The ONS said the U.K. economy is now 2% smaller than it was before recession struck in 2008, not 2.5% as previously thought.
The economy also appears to have got off to a good start in the final quarter. Data for October showed the services sector, which accounts for the bulk of U.K. output, expanded 2.1% on a year earlier.