EasyJet chief executive Johan Lundgren said: “The report makes clear once again that airlines and passengers were severely let down by NATS due to its failure of resilience and lack of planning.
“Airlines were then left picking up the pieces and costs, which ran into millions.”
The air traffic control system had previously processed more than 15 million flight plans without the scenario being seen.
A NATS spokesman said: “We would like to apologise again for the inconvenience passengers suffered because of this very unusual technical incident.
“Our own internal investigation made 48 recommendations, most of which we have already implemented; these include improving our engagement with our airline and airport customers, our wider contingency and crisis response, and our engineering support processes.
“We fixed the specific issue that caused the problem last year as our first priority and it cannot reoccur.”
Transport Secretary Louise Haigh said: “The NATS IT failure last year was an unprecedented event that we all hope never happens again.
“My department will look to introduce reforms, when we can, to provide air travellers with the highest level of protection possible.”
Under the Conservative government, in June last year the Department for Transport set out plans to give the CAA “stronger enforcement powers”, but no legislation on the issue was introduced to Parliament.