Tea is, today, a quintessential part of British identity but, until 1784, it was reserved solely for the upper classes.
The British upper classes first began to take tea in approximately 1645, when the East India Trading Company began importing it. Britain had a total monopoly on the leaf and thus, it was rare and terribly expensive... made even more so by the 119% tax on it. Thank you King Charles I's parliament. Though tea remained expensive (and locked away in little silver caddies made especially for the purpose), it gradually became part of the lives of most citizens of the British empire (see the Boston Tea Party, for evidence of this).
Tea really entered into the life of the average Brit thanks to (you guessed it!) William Pitt the Younger, who reduced the tax to 12%, making tea affordable to everyone and thus a part of the British national identity. And also making him a hero to the tea-loving Amateur Historian.