Make a large pot of tea, about 900ml (1½pt) or enough for 6 cups. Brew for 2-3 minutes, then remove the teabags. Add the sugar and chill for 1 hour.
Fill a large jug with ice and pour in the sweetened tea. Add the gin (if using) and lemon juice and stir well. Serve in tall glasses or teacups, with lemon slices and some fresh mint to garnish, if you like.