The tradition of British tea started in the 19th century, when only two meals a day were served. A duchess invited friends over for an extra meal, as she was hungry in the late afternoons. The tradition caught on quickly, and two distinct forms of tea service evolved: high and low. Low tea was served in the late part of the afternoon in the homes of wealthy aristocrats and featured gourmet tidbits rather than solid meals, with the emphasis on presentation and conversation. High tea, also known as meat tea, was the main meal of the day of the low and middle classes, consisting of full dinner items such as roast beef, potatoes, peas, and tea.
According to Wikipedia, this duchess was Anna Maria Stanhope, 7th Duchess of Bedford.