I'm not sure if you're being sarcastic or not, but from what I hear some people have had problems, however I've never had any trouble. But they're on strike atm....well there were a few days ago; next one is due soon.
How do you mean legendary? Efficient you mean? not sure about that, you've already noted how small a land mass UK is, and Royal Mail isn't without its problems, but they are quite acceptable in my eye. Then again the majority of my parcels are not delivered by them.