British Airways said it hopes to operate a "near-normal" schedule on Sunday following an IT outage which caused travel chaos for many passengers on Saturday, but reports suggest the disruption has entered a second day, with a third of BA flights from Heathrow cancelled.
The Guardian reports that dozens of services were cancelled on Sunday morning and experts say the disruption could continue for days.
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In a statement, BA said: "Following the major IT system failure experienced throughout Saturday, we are continuing to work hard to fully restore all of our global IT systems.
"We expect some further disruption today, but we are aiming to operate the majority of services from Heathrow and a near normal schedule at Gatwick.
"Please do not come to the airports unless you have a confirmed booking for travel. At this time we are unable to process re-bookings at the airport terminals."
The airline continued: "We are extremely sorry for the significant levels of disruption caused to customers and understand how frustrating their experiences have been."