A "technical problem" at the Swanwick air traffic control centre on Friday morning caused problems at both the London airports, which were already coping with the after-effects of the weather disruption. During the afternoon NATS said it had "fixed the issue sufficiently to safely increase traffic flow rates and will see an improving picture through the rest of the day".
European air traffic co-ordinating agency Eurocontrol said the problem was caused by an "issue with radar displays".
Scores of flights have either been cancelled, diverted and delayed and the authorities at both airports have advised travellers to contact their airlines before travelling to the airport.
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