When I started bike commuting to work, living in Nottingham and working west of Derby, I would take the Red Arrow 'fast' bus from Nottingham to Derby city center, which are big coaches rather than regular low floor buses, and have a cargo hold underneath.
Despite Trent Barton, the bus operator, assuring me that I was allowed to take my bike and put it in the hold, most times I'd try to do it I'd get an irate driver jumping off shouting "oi you can't do that!". Once I even got one 'teach me a lesson' by pretending to drive off (before stopping a few meters later) before I got a chance to take it off. Even after repeatedly asking Trent Barton to please tell their drivers that I am allowed to do so, and even resorting to having to carry around a printed off email from them assuring me I was allowed to which I could show the drivers, I STILL would get grief several times a week.
In the end I just started taking the train.