I had originally gone on about the nature of the uk and national identity and social class but it was off topic and didn’t do justice to the complexity of the issue so ill just be clear where I am on the meals. The class stuff is deeply english.
In Scotland, you start the day with breakfast, have lunch at lunchtime and have tea at teatime. Tea is the evening meal, and can be I suppose anytime as early as 4pm (too late for a late lunch) and as late as 7pm. The same meal after about 7pm would still be your tea; you just wouldn’t be eating it at teatime. Dinner refers to a more formal meal, such as in a (suitably upmarket) restaurant, or had when entertaining guests. Dinner is eaten later in the evening. Not before 7pm. If on the day after someone were to ask what you had had for your tea, you would say what you had for dinner, but not necessarily point out it was dinner. So you if you have a dinner party, you have dinner for your tea. If you have a tea party that’s very different, that would be light food and tea (the drink) sometime during the day. You could have a tea party for elevenses, brunch or afternoon tea, but none of these would be having your tea.
So you can have tea with any meal at any time, have your tea at teatime or after, tea parties must be before teatime and shouldn’t be had for your tea.
“Supper” doesn’t exist, it’s a word made up so that people have an excuse to eat a 4th meal. If your tea is so late that its past teatime or dinnertime, it’s still your tea.