Ryanair boss Michael O’Leary has slammed air traffic control (ATC) provider Nats for the “unacceptable” disruption caused over the past two days.

In a video message, the chief executive described Monday as “a very difficult day” with 250 flights cancelled, while a further 70 were axed on Tuesday.

He said: “We have been in contact with UK Nats.

“We still haven’t had an explanation from them (about) what exactly caused this failure yesterday and where were their back-up systems.

“It’s not acceptable that UK Nats simply allow their computer systems to be taken down and everybody’s flights get cancelled.”