When did British people begin to confuse high tea and low tea?
I would argue that most British people don’t confuse the two. In my experience high tea is usually abbreviated to tea when eaten around 6oclock. Perhaps this is where the confusion arises. Or perhaps it is a regional variation. Tea is a much more substantial meal than afternoon tea. Tea was traditionally eaten by the working class as you suggest, arriving home from work for 6oclock. Perhaps the continued trend for both men and women to work even later, combined with extended travelling times means that people now eat yet later still. I argue that this later meal time and increased wealth also means that most people now eat formal dinner rather than tea as before. Whereas, on weekends and holidays, or if you visit any hotel or resort, afternoon tea is still very popular. Traditionally it is a light meal of sandwiches, pastries and cakes and is eaten around 4oclock. Perhaps our bosses at work will let us stop for afternoon tea to keep up this lovely British tradition!