Airlines are warning of further delays and disruption going into the weekend following the closure of UK airspace on Friday.
A technical problem at the NATS Swanwick control centre grounded flights at London airports this afternoon and had knock-on effects at airports across the country.
NATS said a full investigation was underway to establish the cause of the fault but dismissed initial reports that it was due to a power cut.
In its latest update at 8pm Friday, it said the system has been fully restored but it would take time for operations across the UK to fully recover.
It told passengers to contact their airline for the status of their flight.
British Airways has bought in extra to staff to help customers and has booked a large number of hotels rooms to accommodate those who have been stranded overnight.
"We anticipate that all long-haul services will operate this evening, although there will be delays as the airport recovers from the system failure. Unfortunately, we’ve had to cancel a number of our short-haul flights from Heathrow this evening and we’re working hard to minimise the impact," it said.
Monarch advised customers to expect delays to all flights but to check in as normal.
EasyJet has reportedly cancelled 10 flights to and from Gatwick and plans to cancel another two on Saturday.
Heathrow Airport said flights are experiencing delays and cancellations and said there would be a knock-on effect to some services on Saturday because aircraft and crew will be out of position.
"If you are due to depart today or tomorrow, please check your flight status before travelling to the airport," it told passengers.
The NATS problems come a year after a telephone failure at Swanwick caused huge disruption.
by Bev Fearis
