The continuing chaos follows a computer malfunction in the air traffic control system on Saturday.
The curfew for night time landings was extended until 0230BST on Sunday at London's Heathrow airport in an effort to clear the backlog.
But a British Airways spokeswoman warned that the back-log of flights meant that delays were expected to continue.
"We strongly advise all customers to telephone their airlines to
find out the latest," she said.
Gatwick and Heathrow were worst hit but Manchester, Belfast and Glasgow were also affected.
A spokeswoman for National Air Traffic Services said the computer which went down was not "safety critical".
Deborah Seymour said: "It surrounds what are known as flight strips which contain all the information about a plane's course. These are normally passed electronically but staff were having to manually retrieve the information - basically write it out by hand.
The computer was fixed on Saturday afternoon.
NATS has promised a "thorough investigation" into the computer breakdown, the second time the system has failed in a week.
A spokesman for the Association of British Travel Agents said the computer problem had caused a "nightmare" for holidaymakers.
Airport chaos
British Airways said 60 flights had been cancelled at Heathrow and Gatwick on Saturday.
Budget operator easyJet cancelled all its flights on Saturday, instead offering customers refunds or alternative flights.
Many of the hundreds of people delayed at the UK's busiest airport, Heathrow, were incredulous that a single technical failure could cause problems on such a scale.
Phil Flowers, from Wednesbury, West Midlands, faced a wait of several hours for his flight to Johannesburg.
"I just can't believe they haven't got an effective back-up system," he said.
Ann Jenkins, from Luton, who was bound for Portugal said: "It's been chaos since we arrived. I've had a bad week anyway, so this is just what we didn't need."