Management failure
Not to dismiss any of the technical possibilities that have been discussed here, the single most likely reason for such a catastrophic outage is that IT budgets have been shaved consistently over a period of years to a point where all the senior IT managers understood that their staffing levels, processes and infrastructure were probably going to be inadequate to survive a catastrophic failure or series of failures, but were equally aware that telling their finance and operational colleagues this would probably result in their being side-lined, fired, down-sized or moved to "special projects"...
For an organisation in this state of denial the quarterly bottom-line is everything, and long-term is only the next quarter. You could reasonably argue that this sort of failure is possibly the only way BA's IT investment could ever increase to address the long-term failure to invest responsibly
Biting the hand that feeds IT
