Speaking as a Londoner originally, we always had breakfast, dinner and tea as the three meals of the day. Supper would only refer to a late meal close to bed time, and not a meal at the regular time. Lunch was a word we seldom used.

Afternoon tea is quite a different thing than our evening meal. The latter is really high tea, but we would consider that too pretentious. Afternoon tea, OTOH, which should not be called high tea, was mainly something for the ladies and small children, taking place in the middle of the afternoon, i.e. during the working day. Tea shops serve afternoon tea for tourists, who are on holiday anyway. And yes, AFAIK it still goes on.

Here is a link to a site about the Bristow cartoon strip, specifically to a page about Mr. Bristow's afternoon tea from the tea trolley at work:

http://www.guter.org/tea.htm

This is perhaps anachronistic, as at least as many people now drink coffee, but at one time everyone drank tea during their break.