Update 5:08pm UK time: Air traffic controller NATS says its technical problems have been fixed, but flight delays caused by the glitch are expected to cause severe disruption to flights in and out of London. Airlines are advising travellers to check the status of their flight online. Our original story follows.
Airspace over London has been restricted by safety regulators, following a "technical failure."
The restriction of airspace over the UK's capital will cause potentially severe flight delays, the European Organisation for the Safety of Air Navigation has warned. In a brief statement on its website, the regulator said, "There has been a technical failure at London ACC. Engineers are working on the problem and more information will be given when available. Only already airborne traffic will be accepted."
It was initially reported that London airspace had been closed entirely, however UK-based National Air Traffic Control (NATS) clarified, "UK airspace has not been closed, but airspace capacity has been restricted in order to manage the situation. We apologise for any delays and our incident response team has been mobilised."
The airspace restriction -- caused by a technical problem at Swanwick air traffic control centre -- is likely to cause severe disruption to those due to travel in or out of London, with scheduled flights now backing up in the wake of the computer glitch, and airlines telling customers to prepare for delays.
Heathrow airport, which is the UK's busiest airport, handled an average of 1,286 flights per day in 2013, while a whopping 4.4 million passengers travelled through London's second-biggest airport, Gatwick, in August 2014.
While knock-on delays due to the computer failure may last well into the night, NATS confirmed at 4:21pm UK time that it was "in the process of returning to normal operations", having fixed the computer glitch.
System has been restored and we are in the process of returning to normal operations. For more information please see http://t.co/2ToleaTUrH— NATS (@NATSPressOffice) December 12, 2014
In terms of handling delays, analysts speaking to BBC News have suggested that long-distance flights are likely to take priority over shorter, domestic journeys.