I note that the ba website states:
Please keep any food, transport or accommodation receipts and you can make a claim in due course through our Customer Relations teams.
Whereas the CAA has already issued its own statement:
Commenting on the delays and cancellations affecting British Airways passengers, Matt Buffey, Head of Consumer Protection at the Civil Aviation Authority, said:
"Passengers affected by the disruption to British Airways' flights are protected under EU law. The welfare of passengers must be the priority for any airline experiencing disruption and we fully expect all UK airlines to meet their obligations.
Passengers who are currently caught up in this disruption should be informed of their legal rights by British Airways, but they can find out the full details of their rights during delays and cancellations by visiting the CAA website."
So waiting for ba to sort out claims through fistfuls of receipts won't be an adequate response. The CAA has clearly decided that ba's passenger delays were
not caused by 'extraordinary circumstances'; the EU law on flight compensation uses the term 'extraordinary circumstances' to refer to situations where delays or cancellations have been caused by things that are not the responsibility of the airline, whereas the airline clearly is responsible for its IT systems having sufficient resilience and redundancy.
Thus full compensation under EU law must be paid.