Slice the lemon almost in half, and take a single round slice from the middle to garnish. Juice the two halves.
Place the tea bags and mint sprigs in a large jug. Pour boiling water over them and leave to steep for about 8 minutes. Remove and discard the tea bags and mint leaves, squeezing them to extract all the flavour.
Add the sugar and stir until it has dissolved. Pour in the orange juice, lemon juice and cold water.
Serve over ice cubes, garnished with mint leaves and the thin slice of lemon.