Passengers at Heathrow and Gatwick were still experiencing delays on Friday evening following restrictions on London airspace after a computer failure at air traffic control body Nats in the afternoon.

Nats confirmed a “technical problem” at its Swanwick control centre in Hampshire caused by a power outage, but said: “Airspace is [now] open.

“We’re restricting traffic volumes in accordance with capability we currently have in our system.”

By 17.00 Nats reported: “The system has been restored. However, it will take time for operations across the UK to fully recover.”

It recommended passengers contact their airline to check the status of their flight.

Nats apologised for any delays and inconvenience.

Heathrow reported late Friday afternoon: “Flights are currently experiencing delays. We will update passengers as soon as we have more information.”

Gatwick airport announced: “Flights are departing but there are delays due to the Air Traffic Control computer issues.”

Pan-European airspace body Eurocontrol earlier warned of “potentially severe delays”.

Eurocontrol revealed: “There has been a failure of the flight data computer server at London ACC [area control centre].

Early reports suggested restrictions could be in place until 19.00 GMT.