It operated all flights from Gatwick, with some hold-ups.

British Airways said that it had cancelled all its flights out of major London airports Heathrow and Gatwick after an IT systems failure, warning people not to travel to the congested hubs.

"Passengers caught up in this disruption should be informed of their legal rights by British Airways, but they can find out the full details of their rights during delays and cancellations by visiting the CAA website".

The airline says it will refund or rebook customers affected by the IT failure, which BA officials believe was caused by a power-supply issue rather than a cyberattack.

The CEO of British Airways, Alex Cruz, told Sky News the IT outage that grounded flights and stranded passengers was due to a power surge that affected messaging across their systems.

It appears to have been so strong that it rendered the back-up system ineffective.

"New technology will be utilised to increase efficiency and simplify the operations", said the British Airways annual report released in December.

"I know this has been a frightful time for customers".

The compensation is not automatic - customers have to write a letter of complaint to the airline.

Cruz said: "At the moment, we do not have a complete picture of what happened".

BA has rejected a suggestion by the GMB union that the outsourcing of IT functions to India to cut costs had contributed to the chaos.

After the outage caused more than 1,000 flights to be delayed or cancelled, including BA's sister airlines in Spain, Iberia and Air Nostrum, focus quickly turned to Mr Cruz's handling of the company, having shut down the airline's computer department past year, slashing 700 jobs in the UK. "Passengers looking to re-book flights should go to ba.com". She added that one of the shops had sold out of food. "We can only feel genuinely sorry for the tens of thousands of passengers who are stranded at airports and face having their travel plans and holidays ruined".

Under EU law customers whose flights were delayed or cancelled are entitled to assistance and compensation. Most "long-haul flights" set to land in London on Sunday are expected to arrive as scheduled, the airline said.

"This is not like an ash cloud or traffic controllers' strike that can't be predicted".

"They've all been local issues around a local data centre who have been managed and fixed by local resources", he said.

Air industry consultant John Strickland said: "There's a massive knock-on effect". Crew working patterns are also governed by strict regulations on rest and working hours.

The airline cancelled 13 short-haul flights at Heathrow on Monday.

However, a BA spokeswoman said: "We would never compromise the integrity and security of our IT systems".