A computer failure at the UK’s air traffic control centre has caused widespread flight disruption.
NATS said a “technical problem” has resulted in airspace being heavily restricted.
“Airspace is open. We're restricting traffic volumes in accordance with capability we currently have in our system,” NATS said.
In a statement Heathrow said: “There is a technical problem at the NATS control centre in Swanwick, which is affecting UK airspace. Flights are currently experiencing delays and we will update passengers as soon as we have more information.”
Gatwick said all its departing flights been grounded and other UK airports are reporting knock-on effects.