The "middle class" is quite a recent invention; it arrived with the Industrial Revolution, and is largely Victorian in origin. The growth of commerce prompted a demand for large numbers of clerical workers: people who wore suits and ties to work, and lived in their own homes in the suburbs. These were not aristocrats moving down the scale; these were aspirational working-class folk, who wanted to separate themselves from their background.

Most of us are now pretty-much middle-class. Regional accents have softened; we're all familiar with middle-class manners and customs; farming and manufacturing nowadays employ very few workers. Most of us are more-or-less clerical workers now.