If TSB hadn't been forcibly split off from Lloyds then this wouldn't be an issue.
Any large scale data migration is going to have problems. These problems are exacerbated due to money being involved. Hands up if you've done a data migration of this scale and had zero issues?
I feel rather sorry for TSB in some respects. Forced into existence, they hire a supposedly expert firm to manage their systems and data migration only to have it blow up in their face. So they're paying through the nose for IBM, and now they're having to deal with frauds, fines and legal nonsense too. And try and provide some kind of valuable service to customers.