In Heathrow and Gatwick, London has Europe’s busiest two- and single-runway airports respectively. Both were effectively shut down for much of yesterday, one of the busiest travel days of the year, by what was described as a “technical issue” at NATS, the National Air Traffic Services. The issue was solved in hours but the backlog of cancelled flights – an estimated 1,200 yesterday and hundreds more today – will take days to clear. NATS is a private company that calls itself “a global leader in air traffic management”. It says it handled around 2.5 million flights in and out of the UK per year before Covid, and that it provides flight management services elsewhere in Europe and in the Middle East, North America and Asia. A modest proposal for NATS: invest in a complete back-up system to which you can switch next time this happens. And for the UK government: insist on it, or take back responsibility for air traffic control.