News Summary

• Air traffic control failure was caused by a "software defect," Nats says.
• The problem happened "in the space of a millisecond", Nats said.
• The failure led to more than 2,000 flights being cancelled and hundreds of thousands of passengers affected.
• Nats chief executive Martin Rolfe said he would not resign, saying the defect was "very, very obscure" The transport secretary described the disruption as "completely unacceptable" and "frustrating" for passengers, airlines and airports.