The disruption began in the morning on Wednesday, July 30, after a technical fault at the NATS control centre in Swanwick.
A NATS spokesperson said: “This was a radar-related issue which was resolved by quickly switching to the back-up system during which time we reduced traffic to ensure safety.
“There is no evidence that this was cyber related.”
Transport secretary Heidi Alexander held talks with NATS chief executive Martin Rolfe.
She said: “I have spoken with NATS CEO Martin Rolfe who provided further detail on yesterday’s technical fault.
“This was an isolated event and there is no evidence of malign activity.
“I will continue to receive regular updates.”
Southampton Airport said yesterday that it was aware of the issue but that none of its flights had been cancelled.
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The back-up system remained in use by controllers on Thursday as investigations continued.
The ATC failure affected the majority of England and Wales for around 20 minutes, causing similar disruption to that seen during severe weather.
Aviation data firm Cirium reported that 84 departures and 71 arrivals were cancelled at UK airports up to 10pm on Wednesday.
Several flights were diverted to other European airports.
Ryanair has called for Mr Rolfe’s resignation, claiming “no lessons have been learnt” since a similar incident in August 2023.
Neal McMahon, chief operating officer at Ryanair, said: “It is outrageous that passengers are once again being hit with delays and disruption due to Martin Rolfe’s continued mismanagement of NATS.”
Business minister Gareth Thomas was asked whether Mr Rolfe would be “fired” following the incident.
He told Times Radio: “Clearly, an incident happened two years ago and measures were taken then.
“It looks like those measures weren’t enough but we need to get to the bottom of what exactly happened, and conversations will take place today.”
