A previously unknown software defect in the UK’s air traffic control system corrupted flight data within milliseconds, triggering a six-hour outage and widespread cancellations and delays. The disruption affected hundreds of thousands of passengers, prompting ministers and airlines to question why the fault was not identified sooner and whether Nats is fit for purpose.

The error began at 10am but was not declared a major incident until 12.32pm, before the system failed completely at 1.32pm and full operations resumed at 7.30pm. More than 2,000 flights were cancelled, and it took over two days to clear the resulting backlog; Nats said a temporary mitigation was in place while a permanent fix undergoes safety testing, while the Civil Aviation Authority will investigate.