Pimm's cup de John Spottiswood

This is the liqueur that the upper crust of British society drinks at polo matches. It's bittersweet and very potent. There used to be several varieties of Pimm's, based on gin, whiskey, rum, brandy, and vodka, but only the one based on gin, called Pimm's No. 1, is still being produced. Serve it with club soda and a bit of lemon juice and garnish with cucumber and celery.