LONDON - A computer failure at an air traffic control centre sparked travel chaos in Britain on Friday as the peak Christmas season gets underway, officials said.

Heathrow Airport, Europe’s busiest hub, said 50 flights had to be cancelled and warned passengers to check their flight status before setting off.

After more than an hour in which some departures were blocked and arrivals diverted, Britain’s National Air Traffic Services (NATS) said the system had been restored and services were returning to normal. The London airports system is the busiest hub in the world with around 135 million passengers a year.

Other British airports were also affected, including Bristol, Edinburgh and Leeds.

‘Disruption on this scale is simply unacceptable and I have asked NATS for a full explanation of this evening’s incident,’ transport minister Patrick McLoughlin said. Brussels-based Eurocontrol, which earlier reported that airspace over London had been shut down, said a ‘measured recovery’ was underway. NATS had earlier said that it was ‘restricting traffic volumes’ following a technical problem at the Swanwick control centre in southern England.

‘UK airspace has not been closed, but airspace capacity has been restricted in order to manage the situation,’ it said in a statement on its website.

Air France said around 20 of its flights were affected, including one flight headed for Dublin which was forced to turn back to Paris. Two Iberia flights that left Madrid for London also returned to their departure point.

Heathrow Airport said in a tweet that the failure was caused by a ‘power outage’, while British media reported that there had been a ‘radar display issue’. This is not the first time that a technical failure at Swanwick has caused travel chaos. Hundreds of flights in Britain and Ireland were delayed or cancelled last year due to a similar problem.