From the opposite point of view
I've known several people that worked in IT at the other financial institution acquired by the Spanish.
Apparently they like to drive the IT policy from there.
As it's 'their' system and apparently has worked for them, they have no doubt jumped to the conclusion that it would just be a plug and play job, until of course they got the call from the UK to tell them it wasn't going according to plan (assuming there was one).
Let's hope they don't let the techies go as it does sound like it's proving to be somewhat of a Herculian effort to put right.