Departing flights from Gatwick and Stansted are facing delays of up to two hours after issues within UK air traffic control.
A Stansted spokesman said all departing flights are subject to delays of between 30 minutes and two hours.
Gatwick Airport said 20 per cent of its departures were experiencing delays, with passengers warned they could wait for a "couple of hours".
The airport said there were currently no issues with arrivals.
Passengers are advised to check with their airline for the latest situation.
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