Airlines are seeking assurances that there will be no repeat of Saturday’s air traffic control computer glitch which led to chaotic scenes at airports as flights were delayed and cancelled leaving thousands of passengers stranded.

The National Air Traffic Service (Nats) issued an apology to those affected by the outage which affected up to 30,000 passengers as more than 200 flights were cancelled.

Ryanair led the criticism of Nats as Abta warned that passengers caught up in the chaos would not be entitled to compensation.

A spokeswoman told the BBC: “In a situation like this it’s not actually deemed to be the airlines’ fault.”

The worst affected airport was Heathrow which suffered from knock-on effects yesterday with 18 flights cancelled.

Others such as Stansted and Gatwick said services had returned to normal by yesterday

Airports affected on Saturday included Manchester, Birmingham, Leeds/Bradford, Doncaster Robin Hood, Belfast International, Dublin and Newcastle.

Ryanair said 300 of its flights had been delayed on Saturday, with 12 cancelled.

It criticised Nats, saying: “While we acknowledge problems can occur, where is the contingency?”

Delays at Stansted averaged two to four hours on Saturday, a spokeswoman said.

The fault occurred when the Nats computer system was making the switchover from the quieter night-time mode to the busier daytime setup.

It was unable to handle the normal volume of flights for a Saturday and said it dealt with 20% fewer than it would have expected.

Nats said: “The reduction in capacity has had a disproportionate effect on southern England because it is extremely complex and busy airspace and we sincerely regret inconvenience to our airline customers and their passengers.

“To be clear, this is a very complex and sophisticated system with more than a million lines of software. This is not simply internal telephones, it is the system that controllers use to speak to other ATC agencies both in the UK and Europe and is the biggest system of its kind in Europe.

“This has been a major challenge for our engineering team and for the manufacturer, who has worked closely with us to ensure this complex problem was resolved as quickly as possible while maintaining a safe service.”