British Airways has cancelled all flights from Heathrow and Gatwick because of global computer problems.
A “major IT system failure is causing very severe disruption to our flight operations worldwide”, the airline said.
It apologised for the “global system outage” and said there was no evidence of a cyber attack.
The GMB union has suggested the failure could have been avoided, had the airline not outsourced its IT work.
BA refuted the claim, saying: “We would never compromise the integrity and security of our IT systems”.