Upon moving to the central belt, and ingratiating myself into more middle class circles of friends I then discovered:
Breakfast - eaten usually when you get up in the morning, say early morning until ~1030am
Lunch - eaten from 12pm until ~2:30pm
Afternoon Tea - taken from around 3:30pm until 4:30pm (cakes/biscuits [cookies] and would also include some kind of sandwich - often cut into triangles)
Tea - 5pm until 6pm - usually a lighter two course meal (say an omlette) and some pudding (desert).
Dinner - taken from 7pm until perhaps 9pm - this would be a fully laiden two or three course meal.
Supper - taken from around 10pm until around 11pm (or just before bedtime) - likely cheese on toast or crackers & cheese and a cuppa.
Obviously you don't need to have every one of these meals every day of the week.