The meltdown hit check-ins, baggage reclaims, the website and even phone lines. More than 300,000 travellers were left seething after cancellations and delays at Heathrow and Gatwick.
Experts predict BA could face a £300million compensation bill. The whistle-blower insisted the IT could have been avoided.
The source added: “There was a sense behind the scenes that something big was about to happen.