"Events in Ukraine are weighing on the internationally exposed manufacturing sector," and the "expansion will get more lopsided in the next couple of quarters," said Rob Wood, an economist at Berenberg in London. "Once tensions ease, business confidence and investment can rebound across Europe, returning some balance to the U.K.'s strong expansion."
Britain has completely recovered the output lost during the financial crisis and is on track to be the best-performing Group of Seven economy this year, with the BOE predicting growth of 3.5 percent.
"The government's long-term economic plan is working," the Treasury in London said in a statement. "But the job is not yet done."
Growth in the second quarter was driven by the dominant services sector, which expanded 1 percent. Industrial production rose 0.3 percent instead of the previously reported 0.4 percent, with manufacturing gaining an unrevised 0.2 percent. Construction output was unchanged. It was initially estimated to have contracted by 0.5 percent.
The ONS said the upward revision to construction helped boost GDP growth in the second quarter to 0.83 percent from the 0.8 percent previously reported. Services output was also slightly higher than previously estimated.
The figures omit GDP by spending, which are usually included in the second estimate, because the ONS is due to publish changes to the way it calculates the national accounts next month.
The risks to the recovery were underlined Thursday by figures showing the 18-nation euro region, which bought 45 percent of British exports last year, posted zero growth last quarter as its three biggest economies failed to expand. The German economy shrank, France stagnated and Italy succumbed to its third recession since 2008.
Unrest in Iraq and Gaza and international sanctions against Russia over its support for rebels in Ukraine are weighing on global outlook.
The stagnation in the euro area "has raised concerns about the fragility of the region's economy and its lack of resilience to shocks such as those posed by Russia," Chris Williamson, chief economist at Markit, said in a statement.
In Britain, a stronger pound is making it harder for British goods to compete on world markets, the housing market is showing signs of slowing and inflation is set to outpace wage growth for a seventh year. The BOE said it expects growth to moderate in the third quarter.
"Geopolitical risks have intensified, and structural adjustment continues in the euro area, where growth is expected to be modest," Carney said this week.
Investors are fully pricing in a quarter-point BOE rate increase by May, Sonia contracts show. Bets had centered on February before the BOE released its latest assessment on Aug. 13.
— With assistance from Harumi Ichikura, Mark Evans and Jillian Ward in London.