More than 330,000 passengers have been affected by a major failure of Britain’s air traffic control system, prompting airlines to demand urgent improvements. A technical problem at National Air Traffic Services (NATS) caused widespread disruption, with significantly more than a thousand flights cancelled and another thousand delayed. Heathrow was particularly badly affected, while disruption continued after engineers resolved the initial fault as airlines struggled to reposition aircraft and crews. Transport Secretary Heidi Alexander said a cyber attack had been ruled out but believed the four-hour outage was not unavoidable. She has asked the Civil Aviation Authority to investigate the resilience of NATS systems and progress on planned upgrades. Airlines have reacted angrily, noting that this is the third serious technical failure in three years, with some calling for chief executive Martin Rolfe to resign. NATS has apologised and promised a full investigation, but passengers have continued to face cancellations and delays.