Tea was first brought to England by the Dutch in the 1650s. However, the ritual of afternoon tea did not begin until 1840.
Anna, the seventh Duchess of Bedford, experienced "sinking feelings" every afternoon around 4, during the long interval between lunch and dinner, which was served at a fashionably late hour. She asked that a tray of sandwiches, cakes and tea be sent to her boudoir. It soon became a habit, and Anna began inviting her friends to join her.
Later, afternoon tea moved from the boudoir to the drawing room and became a time for social visits after the afternoon carriage ride. Traditionally, afternoon tea is still served between 4-6 p.m. It may be very casual - just a cup of tea and something sweet shared with a friend. Or it may be elegant - using the best table linens and china, and serving tea sandwiches and sweets, to celebrate a birthday, an engagement or a christening. Afternoon tea is not a meal so much as an experience - a step back in time to a more gracious era.
<A wonderfulwebsite to learn more about tea and I really enjoyed this one - lots of links>
Living History: the Roanoke Beacon, Plymouth, Washington Co, NC; Apr 1999, pg 4 "Sip tea at historic Latham House"