Just for balance ...
When my late father died, transferring the car registration into my name was hassle free. As was cancelling his drivers licence. Gold star.
When I wanted details of a car's registered owner (because they'd bumped mine and someone got their number), although slow (especially since I forgot to include a photo of my damage and they returned the application) but they provided it.
In fact, I don't think I've ever actually had a problem with them ... except oh yes, there was that time ...
My old Land Rover is still officially diesel even though it's now petrol - DIY engine change. They won't accept my notification without me going and paying someone to confirm the change, something which on principle I refuse to do. I don't actually care - I've notified them which is all the law requires, and their letters back prove that they have received such a notification.