Passengers are facing delays after a computer failure which caused problems for flights in and out of London for a period this afternoon.
Air traffic control body NATS said in a statement: "NATS can confirm that a technical problem has been reported at Swanwick air traffic control centre. We apologise for any delays and our incident response team has been mobilised. Every possible action is being taken to assist in resolving the situation and to confirm the details."
But it added in a tweet that London's airspace is not entirely closed.
Airspace is open. We're restricting traffic volumes in accordance with capability we currently have in our system.
- NATS (@NATSPressOffice) December 12, 2014
European air traffic control body Eurocontrol said there has been a failure of the "flight data computer server" in London, and that "Only already airborne traffic will be accepted."
Heathrow Airport confirmed in a tweet: " Flights are currently experiencing delays due to a power outage at NATS control centre affecting UK airspace."
Gatwick also confirmed in a tweet: "Air Traffic Control is currently experiencing computer issues affecting flight departures at all London Airports."
Update: At 4.15pm NATS said that "following a technical failure at Swanwick, the system has been restored and we are in the process of returning to normal operations."
Update 4.30pm: NATS now says the system has been restored. "However, it will take time for operations across the UK to recover so passengers should contact their airline for the status of their flight."