Update issued at 12.35 BST:
NATS has identified and corrected the technical problem that has been affecting air traffic control systems in the south of England.
Operations are now returning to normal and we are working with the airports, airlines and Eurocontrol to clear the backlog of flights to ensure disruption is kept to a minimum.
Outbound delays from the UK have generally been limited to 20 minutes.
We regret any inconvenience this technical problem has caused, however our first priority will always be the safety of the flying public.
NATS is 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 NATS is 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.
NATS is taking every step to restore services and has contingency plans in place to minimise any disruption.
More information will be released as it becomes available.
Air traffic controllers at Gatwick Airport handled a total of 913 movements on 24 July, breaking their own world record for air traffic movements in a single day from one runway.
NATS is the UK's leading provider of air traffic control services. Each year we handle 2.2 million flights and 220 million passengers in UK airspace.
In addition to providing services to 14 UK airports, we work in more than 30 countries around the world spanning Europe, the Middle East , Asia and America.