There's some grey areas, but broadly if you imagine a company in a tower block.
Right at the top - upper class - The owner
Never comes in, doesn't really know the business, inherited it from her great great uncle, she's a distant cousin of Prince Edward and her family and the royals are connected. Hasn't ever really done any kind of work, handed education, handed businesses, handed houses etc.
Below her on the next floor down are the board members and CEO of the company. These folks went to the same expensive schools as the owner, they don't really understand the nuts and bolts of the business, but they enjoy golfing with the owner and feel like they should be upper class too, but they're not, not really, they're upper middle class...
Then the departmental managers who run the seperate divisions as they're very well educated in the sections they run like solicitors in legal, HR execs and accountants running accounting etc they know what the business as a whole actually does. The middle class, seek to get up the ladder, but often get overlooked as they lack connections as they were educated in state schools and The Universities Of ArseNowhereState or Coventry etc
Then comes the general office workers, receptionists, admin staff, data input, clerks etc The hands on machine workers manufacturing the product the company actually sells are here too, as are the drivers shipping the product, the janitorial staff and maintenance guys, the working class. Sometimes promoted up the tower, but always feel like they're still working class and often vocally champion that fact to anyone that will listen, even after 30 years of working their way up the company...
But....
then there's the people on the outside of the company, the homeless guy in the doorway starving in the cold, the unemployed person that's borrowed money to buy a short to interview for a job there.
The people unable to work there due to circumstances like sickness, disability, caring duties etc. These people are often also called working class. Sometimes they're referred to as the 'under class' channel 5 make programs about how cushy and comfortable life is relying on benefits, foodbanks and living in sink places that they're put. This class seemingly exist for the workers of our company to point at and ridicule but also to live in fear of becoming. Our imaginary company workers see the 'under class' and it's reinforced with poverty porn TV shows that they will end up like "Those people" if they don't tolerate any levels of abuse, pressure and workload. They're laughed at in the company, but feared in private as the wise people of our imagined company know that, should the company faulter and close, they're not too far from 'under class' themselves...