Heathrow Airport has said its services will "remain significantly disrupted" on Tuesday after air traffic controllers across the UK experienced a technical fault.
In a statement about the "technical issues" that affected the National Air Traffic Services (NATS), Britain's busiest airport urged passengers to contact their airline before travelling to the airport.
"The issue has been resolved, however schedules remain significantly disrupted," it said.
"If you are travelling on 29th August, please ensure you contact your airline before travelling to the airport."
London Gatwick has said it plans to operate a normal schedule on Tuesday following the disruption.
However, passengers have been advised to check the status of their flight with their airline before travelling to the airport.
London Stansted also said it planned to run a normal flight schedule on Tuesday, but added "our terminal may be busier than anticipated".
And major UK airlines such as Tui and BA warned of "significant delays" for passengers amid changes to schedules.
By Monday afternoon 232 flights departing UK airports had been cancelled along with 271 arriving flights, according to aviation analytics firm Cirium. It equates to about 8% of all expected departures and 9% of expected arrivals, Cirium added.
The technical fault meant flight plans had to be input manually by controllers.
Transport Secretary Mark Harper said on Monday that "despite resolving the technical issue behind today's air traffic control issues, flights are still unfortunately affected".
He said he would encourage all passengers to read the UK Civil Aviation Authority's guidance and "be aware of their rights when flights are delayed or cancelled".
Technical issue 'remedied' but travellers face continued disruption
Earlier on Monday NATS said the "technical issue" affecting its flight planning system had been "identified and remedied", but travellers continued to face disruption.
"We are now working closely with airlines and airports to manage the flights affected as efficiently as possible," NATS said.
"Our engineers will be carefully monitoring the system's performance as we return to normal operations.
"The flight planning issue affected the system's ability to automatically process flight plans, meaning that flight plans had to be processed manually which cannot be done at the same volume, hence the requirement for traffic flow restrictions.
"Our priority is always to ensure that every flight in the UK remains safe and we are sincerely sorry for the disruption this is causing. Please contact your airline for information on how this may affect your flight."