Re: Big bang
Correct, although TSB and Lloyds continued to use the same systems (well, TSB a copy of the Lloyds systems) to ease the spinoff process. TSB/Sabadell had a choice: Either continue to pay some other bank (Lloyds) for access to the system (which didn't get the improvements that Lloyds' own systems were getting), or build their own. I don't blame Sabadell for choosing the latter... Why contribute to someone else's profits when you know you should have that knowledge in-house.
It's unfortunate that this migration was a massive clusterf***, but ultimately I think TSB and Sabadell will be better off for it.