Afternoon Tea (The traditional 4 o'clock tea)
This is a small meal, not a drink. Traditionally it consists of Tea (or coffee) served with either of the following:

• Freshly baked scones served with cream and jam (Known as a cream tea)
• Afternoon tea sandwiches often thinly sliced cucumber sandwiches with the crusts cut off.
• Assorted pastries

Now most ordinary British families do not have time for afternoon tea at home, but in the past it was a tradition. It became popular about one hundred and fifty years ago, when rich ladies invited their friends to their houses for an afternoon cup of tea. They started offering their visitors sandwiches and cakes too. Soon everyone was enjoying Afternoon tea.

High Tea (The traditional 6 o'clock tea)
The British working population did not have afternoon tea. They had a meal about midday, and a meal after work, between five and seven o'clock. This meal was called 'high tea' or just 'tea'. Traditionally eaten early evening,

High tea was a substantial meal that combined delicious sweet foods, such as scones, cakes, buns or tea breads, with tempting savouries, such as cheese on toast, toasted crumpets, cold meats and pickles or poached eggs on toast. This meal is now often replaced with a supper due to people eating their main meal in the evenings rather than at midday.

Source:http://www.woodlands-junior.kent.sch.uk