An aircraft flies high above Heathrow airport in west London ... a technical problem at the air traffic control centre in Swanwick, southern England, has forced authorities to restrict the airspace above three of London's busiest airports. Photo: Reuters

London: British airports were plunged into chaos on Friday by a technical failure that forced authorities to restrict access to the country's airspace, the National Air Traffic Service (NATS) said.

"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," it said in a statement on its website.

Air traffic control later said the system had been restored and was in the process of returning to normal.

A screen shot taken from planefinder.net showing almost empty British airspace around London's Heathrow Airport. Photo: AP

Eurocontrol, a European air traffic control body, had earlier said the airspace over London had been closed.

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London's biggest airport, Heathrow, said that no flights were taking off or landing. Gatwick, south of the capital, said flights were departing, but with delays. Stansted airport, the city's third busiest, said in a tweet that departing flights were suspended.

The problems did not immediately appear to be linked to any security threat to the United Kingdom, a government source said on condition on anonymity.

Not pushing tin ... A technical failure at The National Air Traffic Control Centre at Swanwick southern England is likely to cause massive delays going into and out of London. Photo: AP

Heathrow is the world's busiest international airport. Over 67 million passengers travel through it annually on services offered by 90 airlines travelling to over 180 destinations in over 90 countries, according to its website.

Airports in Birmingham and Manchester, in central and northern England, said they were unaffected by the airspace closure and were ready to accept diverted flights.

NATS said it suffered a technical problem at its air traffic control centre in Swanwick, southern England. 

Reuters