A major air traffic control technical failure has caused widespread disruption at airports across the UK, with flights grounded or heavily restricted at some of Britain's busiest hubs.
National Air Traffic Services, better known as NATS, confirmed on Tuesday afternoon that it was dealing with a technical problem affecting its flight processing system.
The disruption hit departing flights at airports including Heathrow, Gatwick, Manchester and Stansted, while other airports including Edinburgh and Birmingham also reported problems.
At Gatwick, all departures were temporarily grounded during the disruption, although flights later began moving again as operations continued at a reduced rate.
Heathrow also reported disruption to departing flights and said it was working with NATS to resolve the problem as quickly as possible.
UK airspace remained open
Despite the scale of the disruption, UK airspace was not closed.
NATS said flights were still departing and that airspace remained open, but warned that recovery would take time as engineers worked to restore normal operations.
The company said the fault was within its flight processing system and apologised to passengers affected by delays.
Passengers were advised to check directly with their airline before travelling.
Gatwick departures temporarily grounded
Gatwick was among the airports most visibly affected by the failure.
ITV News reported at 2.39pm that all departures from the airport had been grounded because of the ongoing technical problems with air traffic control equipment.
Aircraft subsequently began departing again, but significant delays and cancellations continued as the aviation network attempted to recover.
Heathrow departures disrupted
Heathrow confirmed that the NATS technical issue was affecting departing flights.
The airport initially said arriving flights were not affected and apologised to passengers caught up in the disruption.
Other airports including Manchester, Stansted, Edinburgh, Birmingham and Belfast were also affected, while disruption was reported to flights involving Dublin and other European airports because aircraft heading for Britain could be delayed before departure.
Knock-on disruption across European network
The failure also had consequences beyond the UK because Britain's busiest airports form a major part of the wider European aviation network.
Flights bound for the UK can be held at their departure airports when air traffic flow restrictions are imposed, creating delays elsewhere in Europe even where local airport systems are operating normally.
Air traffic within the London flight information region was heavily regulated during the incident.
Transport Secretary apologises
Transport Secretary Heidi Alexander acknowledged the disruption and apologised to passengers affected.
The incident is likely to renew scrutiny of the resilience of Britain's air traffic control infrastructure following previous major NATS technical failures.
NATS said engineers were working urgently to restore normal operations, with passengers warned that disruption could continue even after the underlying technical problem was resolved because aircraft and crews had been displaced across the network.