TSB's parent company had appointed an offshore 3rd party to implement the work. The CEO of TSB had hired IBM because he did not trust the offshore company's ability to deliver anymore. I agree it's likely going to cost even more in technical debt and/or setbacks if they bring in fresh eyes at this point!
The CEO brought IBM in this week to clean up the mess.
It doesn’t appear they were involved in the original migration.
The big support contacts started rolling in years ago. I know, because I was there.