The hours-long shutdown on Tuesday, which resulted in the cancellation of more than 1000 flights and left hundreds of thousands of passengers stranded, has ramped up pressure on air traffic control provider NATS and its boss Martin Rolfe.
Ryanair, Europe's biggest airline, had already called for him to resign for his role in the last system meltdown in August 2023, when cancelled flights cost operators STG100 million ($A187 million).
As operations restarted, Heathrow Airport, near London, said passengers should check with their airline before heading to the airport as schedules would have changed due to the problems on Tuesday.
"We are expecting knock-on impacts as aircraft and crew reposition," the UK's busiest hub said in a statement.
"We know how frustrating this situation is and ... are working closely with our local NATS team and airline partners to recover normal operations as quickly as possible."
London Gatwick, Britain's second busiest airport, also advised passengers to check with their airline first.
Ryanair said around 150,000 of its passengers had been affected by the outage after it cancelled more than 200 flights, while British Airways said it had cancelled or diverted 100 flights with tens of thousands impacted.
NATS said the issue, which had impacted its flight data processing system, had been resolved.
Rolfe told Sky News that NATS hadn't "fully done the investigation" to find the reason behind the technical issue that caused the disruption.
"We don't have an idea yet of exactly what went wrong," Rolfe said.
Foreign Secretary Ed Miliband said the UK cannot have a repeat of the disruption.
"First of all, I want to apologise to all of the passengers who have faced disruption," Miliband told the BBC.
"This is frankly unacceptable. It was a problem at the National Air Traffic Service, but we can't have this happen again.
"The Transport Secretary is calling in the head of the Nats, the National Air Traffic Service, (on Wednesday) morning to get answers to this."
Britain's aviation regulator said it would expect NATS to share a full report of the incident.
with AP and PA
