"The recovery from today's system problems has taken longer than we had hoped," announced the British air traffic control service Nats, noting that air traffic has been able to resume.
Heathrow Airport, one of the world's ten largest in terms of passenger traffic, along with Gatwick, East Midlands, Birmingham, Liverpool and Manchester, are among the many airports affected by the problems.
The airline Ryanair, with 50 flights cancelled, says that 65,000 of its passengers have been affected.
UK Transport Minister Heidi Alexander writes on X that she is now "seeking assurances that lessons have been learned and that the systems that support air traffic are up to the job."
