Flights hit by air traffic delays
Some flights into London airports were delayed because of problems with air traffic control equipment.
A spokeswoman for Air Traffic Control (NATS) said its usual monitoring system had failed and flight details had to be input manually.
The system was restored at about 09:00 BST. The spokeswoman apologised for any disruption caused to the airports, including Heathrow and Stansted.
Most of the flight delays were less than an hour.
A spokeswoman for Heathrow Airport said that to maintain safety, some restrictions had been applied to flights at London airports but urged passengers to check in as normal.
Southampton, Gatwick, London Luton and Stansted airports said the problems had also affected some of their flights.
The NATS spokeswoman said the back-up system for processing flight plans was a "much slower process" and said they "regretted" any delays that were caused.