This article implies that middle-class means jobs like radiology technician, phlebotomist, nurse technician. Those don't strike me as middle-class whatsoever!
To me middle-class means privately educated, own reserves of money, probably a large house in the country as well as an apartment in the city, two kids, a labrador and a Barbour quilted jacket: bankers, doctors, baristers etc.
Then beyond that people like the Duke of Westminster, Bill Gates, the Kennedys etc are the upper class - not random Google engineers who joined in the last few years like some US people seem to imply!