Re: Big bang
When was the last time a bank split in two?
Citizens Financial Group was split off from Royal Bank of Scotland, but that was their US division and probably pretty separate anyway, but one single integrated division of a company being split in two; that has never happened. So nobody has experience of it.
The other thing; Sabadel didn't buy TSB off Lloyds. If they had, they would have negotiated much better terms for the IT stuff. TSB was spun off as a separate company and sold on the stock exchange. Then Sabadel took it over a couple of years later.