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.
Following the eruption overnight, the Icelandic Met Office has now reduced its aviation warning level near the Bardarbunga volcano to orange.
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