I am not sure what middle class values are in this context, I have found that many people from both the upper class and from working class [those people that do manual work]still have good manners.
there is a tradition in working mens clubs in the midlands and north of bad manners towards performers, but that does not mean that all upper class and working class people who enjoy other forms of music are rude, people who attend classical concerts are generally polite and they are not all middle class, people who attend jazz concerts or country concerts are generally polite.
in ireland in my experience there is more respect for musical performers from all classes, than there is in England, The working mens club culture has not permeated the irish working class.