Thousands of air travellers faced delays today after air traffic control company Nats experienced "technical problems" at its Hampshire control centre.
The problem led to Nats restricting the number of aircraft flying across the south of England and those taking off from airports.
A Nats spokesman said: "There will be delays, although we are not sure how long they will be."
The problem was at Nats' centre at Swanwick, near Southampton.
The company experienced some flight-affecting computer glitches when it first moved to the site about 10 years ago, but the centre has worked well in recent years.
Nats said today: "We are experiencing technical problems at our Swanwick control centre and we are working to restore full operations.
"This has not resulted in the closure of UK airspace or the suspension of all flights in or out the UK.
"However, to maintain safety, we are restricting the number of aircraft flying across the south of England and those taking off from airports. We regret any inconvenience this may cause; however, our first priority will always be the safety of the flying public.
"We are taking every step to restore services and have contingency plans."