I would say it's regional rather than class based and also depends on certain factors. I'm from South East England (Kent, now Berks) and meals have been termed as follows:
Breakfast - first meal of day, any time up to midday. After that it is brunch or early lunch. The only exception is a Wedding Breakfast which is typically a three course meal mid afternoon. (From the olden days when people married first thing in the morning, around 7-8am, then had breakfast with any guests and any to work for the rest of the day.)
Brunch - see above.
Lunch - meal eaten usually 12-2pm. Can be cold/sandwich type meal i.e. "packed lunch" or a cooked meal i.e. Sunday lunch which is typically a roast. When I was at school (1980s) it WAS called School Dinners if you had the school meal which was a cooked meal served by Dinner Ladies. But if you brought your own sandwiches that was definitely Packed Lunch.
However, my children's schools do now refer to it as School Meals or School Lunches (not dinners) and they have Lunchtime Supervisors not Dinner Ladies.
The only exception now seems to be Christmas Dinner (eaten at lunchtime or early afternoon). Have never heard it called Christmas Lunch.
Tea - certainly some usage in the South but variously.I
Tea is definitely a drink but can be clarified with the prefixes "cup of" or "pot of".
High Tea or Afternoon Tea is typically around 3-4pm. Can be a cup of tea with a slice of cake /scone but if you have Afternoon Tea at a hotel or restaurant it is more of a meal with sandwiches and cakes. High Tea we used to have on Wednesdays and Saturdays at University served at 5pm which was just after team sports finished. That was always bacon and eggs with bread and butter and a massive urn of tea. I've no idea other people have the same idea of High Tea - my Australian relatives liked going for High Tea in a hotel here but it sounded like my description if Afternoon Tea.
It is quite usual to refer to a late afternoon meal (any time before 6), particularly eaten by children and particularly if it's not a hot meal as Tea, as in "would Johnny like to come to tea?" or the " birthday tea" at a child's birthday party.
I would never refer to my evening meal - whether hot or cold - as Tea, if after 6pm.
Dinner - cooked meal eaten in the evening, any time after 6pm. Exception - Christmas Dinner. My daughter goes to an after school club where they have a cooked meal at 5pm and call that Dinner.
Supper - cold or snacky evening meal in place of dinner i.e. soup/sandwiches.