Pimm, a farmer's son from Kent, became the owner of an oyster bar in the City of London, near the Bank of England. He offered the tonic (a gin-based drink containing a secret mixture of herbs and liqueurs) as an aid to digestion, serving it in a small tankard known as a "No. 1 Cup", hence its subsequent name.
Pimm's is most popular in England, particularly southern England. It is one of the two staple drinks at the Wimbledon tennis tournament, the Chelsea Flower Show, the Henley Royal Regatta and the Glyndebourne Festival Opera – the other being Champagne. A Pimm's is also the standard cocktail at British and American polo matches. It is also extremely popular at the summer garden parties of British universities.
(Wikipedia)
2 ounces Pimm's No 1 Cup
5 to 7 ounces ginger ale, lemon-lime soda, or club soda