British Airways said a technical glitch that caused more than 100 flights from Heathrow and Gatwick airports to be cancelled has now been solved.
Passengers said they faced a “bloody nightmare” after 117 flights due depart or arrive were cancelled and more than 200 flights leaving from other locations were also delayed.
Tens of thousands of passengers had their flights cancelled and the airline could face a bill of more than £8 million if all those affected claim compensation under European Union rules.
Businessman Darren Rowe said his flight to Hamburg was cancelled and the response was “pathetic”.
“There were massive queues, it was queue here, queue there, nobody was saying anything," he said.
“You've got young families in that queue, people going to weddings, birthdays, on business. They could have had somebody come around with water updating people about what was going on.”
The fire on the tracks between Victoria and Clapham Junction caused major delays
A British Airways spokesman apologised for the disruption, and said he appreciated how frustrating it had been.
"Our teams have been working tirelessly to get the vast majority of customers on their way, with most of our flights departing," he said.
The airline offered short-haul passengers departing from Heathrow, Gatwick and London City the chance to re-book another flight between Thursday and next Tuesday.
Some passengers struggled to even make it to the airport after Gatwick Express train services from London Victoria were cancelled for several hours after a fire on the tracks.
Gatwick Express general manager Stephen MacCallaugh has apologised for the disruption.