LONDON - The British government has demanded an investigation after a computer failure Friday at one of Britain's two air traffic control centers caused a major disruption of air traffic into and out of London.

The congested airspace over the British capital was closed during the 35-minute shutdown, leading to severe delays and flight cancellations in London and other parts of Europe that officials said would spill over into Saturday.

The problem was traced to the computer system at NATS, the troubled U.K.-based air traffic management company, which has experienced a number of operational problems related to computer issues.

British officials seethed over the system meltdown on a busy Friday afternoon during the run-up to the holiday season, when travel demand is particularly high.

"Disruption on this scale is simply unacceptable, and I have asked NATS for a full explanation of this evening's incident," Transport Secretary Patrick McLoughlin said.

NATS said a computer problem at its center in Swanwick, England, had touched off troubles in the system. After it was fixed, NATS said its operations were returning to normal but would not say how long that would take. It said "further information" about the cause would be released when it becomes available.

Problems were particularly acute at London's Heathrow Airport, Europe's busiest; 66 flights were canceled there as of 6 p.m. local time, with more expected, since planes and flight crews were out of position.