The British Civil Aviation Authority (CAA) on Wednesday extended a no-fly zone over Scotland, Northern Ireland and northwest England because of volcanic ash.
The no-fly zone, which covers airports in Belfast and Edinburgh, was extended from 1300 GMT Wednesday with no estimate from the CAA for a time when the airspace might reopen.
The CAA said, however, that based on current forecasts from the British Met Office, airports in southeast England may not be affected.
The Met Office confirmed that activity from the Eyjafjallajokull volcano in Iceland has increased, and resulted in a rise in ash over British airspace.
Flights over Europe were banned for six days last month because of fears of the effects of volcanic ash on jet engines, causing losses of billions of dollars to airlines.