No one should ever have known that TSB was doing that migration that they cocked up. Whether or not they managed that with Agile methodology (I suspect they didn't) is irrelevant - whoever it was made the decision to do a "big bang" cut over made a massive mistake. They should have migrated to a...
Worth noting (since I haven't seen anyone else call it out explicitly) that "Agile" project management is an umbrella term that covers multiple methodologies and techniques. Scrum is just one, Kanban is another (along with the ******* child of both: Scrumban), Lean, etc.
The first, and probably...