BRITISH Airways said yesterday that it was “closer to full operational capacity” after an IT power cut caused disruption for thousands of passengers worldwide and resulted in flight cancellations at London’s Heathrow and Gatwick airports.

The airline cancelled more short-haul flights from Heathrow yesterday but it has not explained the cause of the problem, which left large numbers of passengers sleeping in airport terminals.

Of those passengers who did manage to get away on the few BA flights that left London, many reported arriving at their destinations minus their luggage.

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.

Mick Rix, the union’s national officer for aviation said: “BA made hundreds of dedicated and loyal IT staff redundant and outsourced the work to India. BA have made substantial profits in for a number of years, and many viewed the company’s actions as just plain greedy.”

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

“IT services are now provided globally by a range of suppliers and this is very common practice across all industries and the UK Government.”

“The root cause was a power supply issue that affected a number of our systems.”

Travellers spent Saturday night spread out over terminal floors after BA cancelled all flights leaving the London hubs. Disruption continued into Sunday and yesterday with dozens more flights cancelled.

Hundreds of travellers flooded King’s Cross station in London in the hope of boarding trains north instead of flying.

Experts say the knock-on effect could continue for several days, with the airline facing huge compensation costs – up to £100 million according to some estimates.

BA’s chief executive Alex Cruz has posted videos on social media apologising for what he called a “horrible time for passengers”, but has also tweeted that he will not be resigning over the issue.

No-one from the airline has been able to answer questions about the IT system crash, and BA has not explained why there was no back-up system in place.

The airline blamed a power cut, but IT experts have said it should not have been enough to cause even a “flicker of the lights” in its data centre.

That centre would have had a disaster recovery plan that should have started up even if the power could not be restored, but one expert said that would have depended in part on long-serving staff with a detailed knowledge of the various systems built up over the years.